the earliest ordovician cephalopods of eastern laurentia - BioOne

J. Paleont., 81(5), 2007, pp. 841–857 Copyright 䉷 2007, The Paleontological Society 0022-3360/07/0081-841$03.00

THE EARLIEST ORDOVICIAN CEPHALOPODS OF EASTERN LAURENTIA— ELLESMEROCERIDS OF THE TRIBES HILL FORMATION, EASTERN NEW YORK ¨ RN KRO ¨ GER1 BJO

AND

ED LANDING2

Museum fu¨r Naturkunde, Humboldt Universita¨t zu Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany, ⬍[email protected]⬎, and 2 New York State Museum, Albany, New York 12230, ⬍[email protected]⬎

1

ABSTRACT—The Tribes Hill Formation (upper Skullrockian) of New York records the earliest Ordovician diversification of cephalopods, in particular ellesmerocerids, on the east Laurentian, shallow carbonate platform. Revision of this cephalopod fauna on the basis of approximately 430 specimens collected across eastern New York has led to new information on inter- and intraspecific variation of the taxa and extensive synonymization of species-level taxa. The Ellesmeroceratidae and Protocycloceratidae, Ellesmeroceras, and Eremoceras are emended, Eorudolfoceras n. gen. and Dakeoceras champlainense n. sp. are erected. A rank abundance plot of the 342 specimens at a locality in the Lake Champlain lowlands provides information on the community structure of the nautiloid fauna, where small orthoconic taxa are shown to dominate strongly. The small orthocone Ectenolites was the most common genus in terms of total occurrences, was the most paleogeographically widespread genus, and was the only genus to cross the Cambrian–Ordovician boundary.

INTRODUCTION

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TRIBES Hill Formation is the lowest Ordovician unit on the northeastern margin of the Laurentian platform in eastern New York and western Vermont (see Landing et al., 2003). This unconformity-bounded, relatively thin (ca. 30–60 m), carbonatedominated unit (Landing et al., 1996, 2003) yields one of the oldest Ordovician cephalopod faunas in North America. This fauna is particularly important because cephalopods experienced their first major crisis in the latest Cambrian (Chen and Teichert, 1983), and only one group, the Ellesmerocerida, survived this crisis to diversify in the Early Ordovician. As a result, Tribes Hill Formation yields an assemblage that represents the earliest efflorescence of the Ellesmerocerida. The cephalopods of the Tribes Hill Formation constitute many of the taxa in Flower’s (1964) monograph ‘‘The nautiloid order Ellesmeroceratida (Cephalopoda).’’ In that report, Flower (1964) erected the order Ellesmerocerida and provided a comprehensive overview of its morphologic and taxonomic diversity. Thus, the Tribes Hill cephalopods were fundamental to proposal of the Ellesmeroceratida. However, the material that Flower (1964) described constituted only a small fraction of what he actually collected in the Champlain lowlands of eastern New York. Flower (1964, p. 1) wrote, ‘‘The writer discovered in 1940 a prolific ellesmeroceroid assemblage in the Smiths [sic., read ‘‘Smith’’] Basin limestone of eastern New York, and over several years accumulated a large collection which it was hoped would supply a basis for a critical study of the extend of variation within the species. Most of this material was the property of the New York State Museum and the writer was informed (Goldring, fide litt.) that it could not be loaned for study. Present descriptions depend upon only a part of the material collected in 1941.’’ More than 60 years later, we have studied the specimens that Flower claimed were inaccessible to him, along with specimens that we recently collected. Consequently, the intra- and interspecific variation of taxa previously based on a limited number of representatives have finally been evaluated. A detailed documentation of the stratigraphic occurrences of the cephalopods within the Tribes Hill Formation provides new information on the community structure of earliest Ordovician mollusks. HE

MATERIAL AND METHODS

Most of the specimens reviewed in this report were collected by R. H. Flower during his tenure at the New York State Museum (NYSM) in the 1940s and are in the NYSM Paleontology Collection. This large, lower Lower Ordovician collection is particularly significant because it will likely never be markedly added

to—Flower was an enthusiastic collector during a time when the activity on small dairy farms kept second growth from overgrowing pasture sections like that at Smith Basin. When Flower (1964) published his ellesmerocerid monograph, he worked at the New Mexico Bureau of Mines and Mineral Resources, and his description of the Tribes Hill fauna was based on the limited material that he took to New Mexico. This material, which includes all of his types, is now in the New Mexico Museum of Natural History (NMBM). Fewer than 10 specimens herein ascribed to Annoceras costatum Flower, 1964 and a specimen of Conocerina reducta (Flower, 1964) is today in the collection of the NMBM, with additional specimens in the National Museum of Natural History of the Smithsonian Institution (NMNH) (see Wolberg, 1990a, b, c). Additional material from the Tribes Hill Formation was collected by D. W. Fisher over several decades of field work (e.g., Fisher, 1954), by E. Landing in regional studies of the unit (Landing et al., 1996, 2003), and by E. Landing and B. Kro¨ger during field work in 2005. All of the latter material is in the NYSM Paleontology Collection. The taxonomy of the Tribes Hill Formation cephalopods was revised on the basis of all available material. Not all species known from the Tribes Hill Formation are in need of a revision because no additional material was available or no new features could be observed. Therefore several species that occur in the Tribes Hill Formation are not re-described herein. A complete list of the species occurring in the Tribes Hill Formation is provided in Table 1. We estimated the goodness of fit of the abundance rank density function by comparison with a lognormal density curve (null hypothesis) by the Maximum Likelihood and Chi-square criteria. This procedure involved use of Regress⫹ 2.5 f (McLaughlin, 2003). GEOLOGICAL SETTING AND PALEOECOLOGY OF THE FAUNA

The Lower Ordovician of eastern New York lies in two terranes. The first is the autochthonous to locally parautochthonous platform carbonates of the Champlain lowland and the completely autochthonous carbonates of the Mohawk and St. Lawrence river valleys. The second is the allochthonous, mudstone-dominated, lower continental slope facies of the Taconic overthrust of easternmost New York (Fig. 1; see Fisher, 1984). Only the autochthonous-parautochthonous carbonates yield cephalopods. The Lower Ordovician autochthonous-parautochthonous carbonates comprise three formations. These formations represent type 1 depositional sequences (Van Wagoner et al., 1988) that correspond to three major eustatic rises across the eastern margin

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TABLE 1—Complete list of nautiloid occurrences of the Tribes Hill Formation, Lower Ordovician, New York. Species-level determination of Eorudolfoceras n. gen., is generally not possible, and occurrences are therefore shown in parentheses. Note the low interference of the species between the Mohawk Valley and the Champlain lowlands. Abbrevations: SM, Sprakers Member; WHM, Wolf Hollow Member; CRM, Canyon Road Member; LCL, Lake Champlain lowlands; MV, Mohawk Valley. #

Cephalopods of the Tribes Hill Formation, Lower Ordovician, New York

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 22 23 24 25 26 27 29

Annoceras costatum Flower, 1964 Annoceras multicameratum (Flower, 1964) Buehleroceras arcuatum Flower, 1964 Buehleroceras infundibulum Flower, 1964 Buehleroceras sinuatum Flower, 1964 Caseoceras obesum Flower, 1964 Clarkoceras ruedemanni Flower, 1964 Clarkoceras trapezoidale Flower, 1964 Clarkoceras whitehallense Ulrich et al., 1943 Conocerina reducta Flower, 1964 Dakeoceras champlainense n. sp. Dakeoceras gracilis (Cleland, 1903) Dakeoceras harrisi Flower, 1964 Dakeoceras mohawkense (Ulrich et al., 1943) Ectenolites clelandi (Ulrich et al., 1944) Ectenolites extensus Flower, 1964 Ectenolites sinuatus Flower, 1964 Ellesmeroceras spp. Eorudolfoceras antiquum (Flower, 1964) Eorudolfoceras praenuntium (Flower, 1964) Eremoceras expansum Flower, 1964 Eremoceras teres Ulrich et al., 1943 Eremoceras trapezoidale Flower, 1964 Eremoceras perseptatum Flower, 1964 Keraiaceras costatum Flower, 1964 Levisoceras cf. edwardsi Ulrich et al. 1943 Paradakeoceras planiventrum Flower, 1964 Paradakeoceras minor Flower, 1964 Walcottoceras cf. obliquum Ulrich et al., 1944

of Laurentia (see Landing et al., 2003). The lowest of these depositional sequences is the Tribes Hill Formation of Ulrich and Cushing (1910). The outcrop of the Tribes Hill Formation extends for almost 400 km along the N-S trend of the Hudson River-Lake Champlain lowlands from Poughkeepsie, New York, to Burlington, Vermont (Landing et al., 2003). However, this report summarizes particularly fossiliferous localities in the southern Lake Champlain lowland between Whitehall and Smith Basin in Washington County, New York (see Appendix). Outcrops of the Tribes Hill are widespread in the central Mohawk River valley (Landing et al., 1996), with numerous outcrops of the formation between

FIGURE 1—Map of New York state showing northern outcrops of the Tribes Hill Formation near the middle Proterozoic Adirondack massif. Tribes Hill Formation near Poughkeepsie, New York, has traditionally been called ‘‘Halcion Lake Formation’’ (Landing et al., 2003).

SM

WHM

CRM

LCL

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⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻

(⫻) (⫻)

⫻

⫻ ⫻ ⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻ ⫻ ⫻ ⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻

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MV

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Hoffmanns and Canajoharie in east-central New York (see Appendix). The Tribes Hill Formation is a deepening-shoaling, unconformity-bounded, carbonate-dominated sequence laid down on a wave dominated shelf (Landing et al., 1996; Landing, 1998). Trilobite and conodont faunas of the Tribes Hill Formation in New York and Vermont (Westrop et al., 1993; Landing et al., 1996, 2003) indicate that the formation represents only a small interval of the lower, but not lowermost, Ordovician (i.e., lower Tremadocian, upper Skullrockian Stage of Ross et al., 1997) (Fig. 2).

FIGURE 2—Stratigraphy of the authochthonous Early Ordovician of New York.

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO

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FIGURE 4—Abundance-rank diagram of the cephalopods collected from the Canyon Road Member, upper Tribes Hill Formation, by R. H. Flower during the 1940s just east of Smith Basin, Washington County, New York (NYSM loc. 5896); compare with Table 2. A goodness-of-fit test, using the Chi-square criterion, shows that the data represent neither a geometric nor a logarithmic distribution. The fauna is strongly dominated by Ectenolites, Annoceras Flower, 1964, and Eorudolfoceras n. gen.

FIGURE 3—Schematic section of the Tribes Hill Formation in eastern New York. Locally the carbonates are dolomitic. The dolomitization varies strongly locally due to hydrothermal controls, and is not shown in the figure.

Landing et al. (1996, 2003) revised the internal stratigraphy of the formation, and proposed four regionally extensive members (Fig. 3). The lower part of the formation is the Sprakers Member. The Sprakers includes intertidal carbonates and shallower wavedeposited fossil (mollusk-dominated) grainstones and calcisiltites in the Mohawk River valley that are laterally transitional into micro-cross-laminated dolomitic, fine-grained sandstones in the easternmost Mohawk valley and Lake Champlain lowlands. The overlying, thin (ca. 1.5 m), recessive Van Wie Member is the deepest facies of the formation, and features dark grey shale with storm-deposited, lenticular, intraclast-trilobite-echinoderm limestones. Increasingly, mollusk-dominated faunas reappear in the

massive, cliff-forming Wolf Hollow Member with its characteristic thrombolites in an echinoderm-intraclast matrix. The uppermost member of the Tribes Hill Formation is the Canyon Road Member. In the Mohawk Valley, the Canyon Road Member (equivalent to the Fonda and Chuctanunda Creek members of Fisher, 1954) includes glauconitic-fossil hash-intraclast-Fe-ooid beds at its base and evaporitic dolostones at its top. In the Lake Champlain area, the Canyon Road member is represented by a succession of sparsely ooid-bearing mud-wackestones. The topmost beds of the Canyon Road member yield a rich mollusk fauna, and is Flower’s (1968) ‘‘Smith Basin Limestone’’ (see Landing et al., 2003). The most diverse, abundant conodont and trilobite assemblages occur in the middle part of the formation—the upper Sprakers, Van Wie, and lower Canyon Road Members. These constitute the deepest and most unrestricted marine facies (Landing et al., 1996). By comparison, trilobite-poor, mollusk-dominated assemblages occur in the lower Sprakers, upper Wolf Hollow, and Canyon Road Members. At the Tristates Quarry just east of Whitehall, cephalopods occur in great abundance together with large ophiletid gastropods at horizon TRQ-32 (see Landing et al., 2003, fig. 4) in the uppermost Wolf Hollow. The diverse gastropod-cephalopod assemblages described by Flower (1964, 1968) south of Whitehall at Smith Basin (NYSM localities 5926, 5896, 5926) represent the Wolf Hollow and the Canyon Road members, respectively (Landing et al., 2003). Both intervals lie in the shoaling upper interval of the Tribes Hill, and are interpreted as a latest highstand systems tract. These intervals were earlier thought to be an intertidal facies (Braun and Friedman, 1969), but Landing et al. (1996) demonstrated that the environment was wave-dominated and somewhat deeper, with frequent storm beds that indicate episodically high-energy deposition. Thus, the peaks in cephalopod abundance and diversity discussed below indicate shallow, but not intertidal environments and a more restricted marine facies than that of the uppermost Sprakers, Van Wie, and lower Wolf Hollow members. COMPOSITION OF THE CEPHALOPOD FAUNA

Revision of the Tribes Hill Formation in New York indicates that it has 29 known species of 15 nautiloid genera assigned to the Ellesmeroceratidae (Table 1). The fauna is highly provincial, with only two of the species known from other regions. The first is Eremoceras teres Ulrich, Foerste, and Miller, 1943, which occurs in the coeval Oneota Dolostone in Wisconsin and the ‘‘Upper

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TABLE 2—Occurrences of nautiloid genera from the Canyon Road Member, upper Tribes Hill Formation, collected by R. H. Flower during the 1940s just east of Smith Basin, Washington County, New York (NYSM loc. 5896). # 1 2 3 4 5 6 7 8 9 10 11

Smith Basin Occurrences Ectenolites Ulrich and Foerste, 1935 Annoceras Flower, 1964 Eorudolfoceras Ulrich et al., 1944 Clarkoceras Ruedemann, 1905 Eremoceras Hyatt, 1884 Buehleroceras Ulrich et al., 1943 Dakeoceras Ulrich and Foerste, 1931 Conocerina Ulrich and Foerste, 1935 Keraiaceras Flower, 1964 Paradakeoceras Flower, 1964 Walcottoceras Ulrich and Foerste, 1935

known to persist through the Cambrian–Ordovician boundary, and thus represents the probable ancestor of all post-Cambrian nautiloids. TERMINOLOGY

144 105 67 18 3 2 2 1 1 1 1

Ozarkian,’’ or Stonehenge Limestone, of Pennsylvania (Ulrich et al., 1943) (Table 2). The second is Ectenolites extensus Flower, 1964—known from the Chepultapec Limestone of Virginia and the Upper Cambrian Siyangshan Formation of south-central China. However, Ectenolites Flower, 1964 is extremely widespread in the uppermost Cambrian to lowest Ordovician, reported from many North American localities in the Lower Ordovician, and thus provides little paleogeographic information. NYSM locality 5896, east of Smith Basin village in Washington County, New York, yielded the largest number of specimens, and probably gives the best representation of the local faunal composition. This locality in the upper Tribes Hill Formation (Canyon Road Member) is Flower’s (1968) type locality of his ‘‘Smith Basin Limestone.’’ The logarithmical plot of the rank abundance graph (Fig. 4) of this collection significantly differs from the trajectory of geometric, lognormal or logit (Fisk) distributions. The latter two distributions, are often recognized in multi-species studies (see Hubbell, 2005; Williamson and Gaston, 2005, and references therein). A test of the goodness-of-fit by the Chi-square and Maximum Likelihood criteria does not confirm the null hypotheses. However, a simple exponential regression of the data reveals a r2 of 0.97, which gives some evidence of a nearly exponential distribution. Compared with an exponential distribution, the right-hand end of the trajectory of the Smith Basin abundance plot is underrepresented, and the left-hand tail is over-represented. Because of the lack of comparable studies of single taxonomic groups within paleocommunities, this plot is difficult to evaluate. However, it illustrates that this particular nautiloid fauna was strongly dominated by a few genera, namely Ectenolites; Annoceras, Flower, 1964; and Eorudolfoceras. Ectenolites and Eorudolfoceras are nearly orthoconic, slender ellesmerocerids. This is remarkable, because the orthoconic conch shape is thought to be more characteristic in later Paleozoic intervals where nautiloid faunas are often dominated by orthoceridans (e.g., Gnoli, 2003). However, Ectenolites is much smaller than characteristic orthoceridans of the later Paleozoic, and reaches adult conch sizes of no more than 10 cm. Orthocones often are assumed to be planktic forms that lived suspended in the water column in relatively distal environments, at least through much of their ontogeny (e.g., Westermann, 1999). This may be true for Late Paleozoic orthoceridans. However, in the Tribes Hill, the nautiloids are strongly associated with a rich benthic mollusk association (Flower, 1968) within the late highstand systems track, while trilobites, a more offshore component of Early Paleozoic faunas (e.g., Westrop et al., 1995), constitute a rare component of the associated Tribes Hill Formation fauna (Landing et al., 2003). Therefore, a demersal lifestyle is assumed for all of the Tribes Hill nautiloids, including the orthocones. Ectenolites must have occupied an important niche in these communities, because the genus is the most common genus in terms of occurrences and also the most widespread nautiloid of this time. It is important to note that Ectenolites extensus is the only ellesmerocerid species that is

The terminology used to describe nautiloid conchs is often imprecise. In order to establish an improved nautiloid taxonomy, refined definitions of some morphologic terms are needed. Position of the siphuncle.⎯The position of the siphuncle is designated with reference to the shell curvature. Thus, the siphuncle can lie centrally or can be shifted toward the convex or concave side of the growth axis, respectively. We use the terms ‘‘prosiphonal’’ and ‘‘antisiphonal’’ to designate the position of a skeletal element of the conch by its relative proximity to the siphuncle. An element is antisiphonal when it is located at the opposite side of the conch with reference to the siphuncle. Siphuncular tube shape.⎯The siphuncular tube consists of segments that span adjacent septa. The tube wall is the connecting ring. The outline of the inner surface of the connecting ring is considered the main character for describing the shape of the siphuncular tube. The siphuncular tube is termed ‘‘concave’’ when it necks, and the minimum cross section of the inner surface of the connecting lies between two adjacent septa. It is ‘‘tubular’’ when the inner cross section of the siphuncular segment is nearly constant between adjacent septa, and ‘‘convex’’ when the siphuncule is inflated between the septa. Connecting ring shape.⎯The connecting ring is described as ‘‘straight’’ when the outer and inner surfaces of the ring are parallel throughout the entire length of the segment, and ‘‘annular’’ when the connecting ring is thickest near the midlength of the segment. The connecting ring can be ‘‘wedge-shaped’’ with its greatest thickness at the adapical end or adoral ends of the segment. SYSTEMATIC PALEONTOLOGY

Order ELLESMEROCERIDA Flower in Flower and Kummel, 1950 Diagnosis.⎯Nautiloids with small cyrto-, ortho-, and gomphoceratoconic conchs, usually laterally compressed or rounded in cross section, generally with short chambers. Siphuncle marginal or submarginal, generally on concave side of growth axis but in some forms at convex side, comparatively wide, sometimes with diaphragms. Connecting ring with concave segments with thick spherulitic to prismatic outer layer. Multiple paired muscle scars located ventrally in living chamber (diagnosis after Kro¨ger and Mutvei, 2005). Discussion.⎯Kro¨ger and Mutvei (2005) emended the Ellesmerocerida and restricted the order to cephalopods with concave siphuncular segments. This restriction excluded the Baltoceratidae (see Mutvei, 2002a, b), the Shideleroceratidae, the Apocrinoceratidae, and several species that were formerly assigned to the Protocycloceratidae. The Ellesmerocerida differ from all other cephalopods in having concave siphuncular segments with their largest diameter at the septal necks. Additionally, the emendation of Kro¨ger and Mutvei (2005) emphasized the presence of serially repeated muscle scars around the adapical end of the body chamber in the Ellesmerocerida. In several ellesmeroceridans of the Tribes Hill Formation, alternating longitudinal striae in the body chamber are interpreted as muscle scars. These features occur independent of the overall conch shape in breviconic, longiconic, cyrtoconic, and orthoconic ellesmeroceridans. We interpret these features as strong support for serial muscle attachment in the Ellesmerocerida. Family ELLESMEROCERATIDAE Kobayashi, 1934 Emended diagnosis.⎯Ellesmerocerids with slender orthoconic to breviconic cyrtocone conchs that differ from the Protocycloceratidae in having a shallow lateral sutural lobe. Siphuncle at concave side of shell curvature. Septal necks are variable, and

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO range from achoanitic, orthochoanitic, hemichoanitic to loxochoanitic. In some forms, septal neck shape differs between growth stages. Septal spacing narrow with more than four septa per length equal to cross section diameter. Comparison.⎯The Bassleroceratidae differ in having a slender, curved shell with a siphuncle exclusively marginal in position and located at the convex side of the conch. The Bathmoceratidae and Cyrtocerinidae differ in having greatly thickened connecting rings, and the Cyclostomiceratidae differ in having a gomphoceratitic conch. The Eothinoceratidae differ in having a strongly thickened, very characteristically shaped connecting ring. Occurrence.⎯Latest Cambrian to Middle Ordovician; cosmopolitan.

Discussion.⎯The emended family diagnosis largely follows Flower (1964). However, the family required an emended diagnosis in order to distinguish it unequivocally from the Protocycloceratidae Kobayashi, 1935. The Protocycloceratidae was originally erected to include slender, straight nautiloids with a marginal siphuncle and annulated conchs. Identical annulated conchs occur homoplastically in very different later Early and Middle Ordovician nautiloid taxa [e.g., in Endoceras annulatum Hall, 1847; Striatocycloceras undulatostriatum (Hall, 1847); Protocycloceras atavus (Brøgger, 1882)]. Consequently, the family served as receptacle for a wide variety of annulated, Early to Middle Ordovician nautiloids with very different septal neck and siphuncular tube shapes. Baltoceratidans with an annulated conch such as Diastoloceras Teichert and Glenister, 1954, and orthoceridans such as Protocycloceras gangshanense Zou, 1988 or P. chaoi Zou, 1988, were assigned to the family. Given this evidence, it is obvious that an annulated conch can hardly serve as the main diagnostic character for a family. We emend the Protocycloceratidae herein in order to provide a classification that is closer to a natural grouping. Thus, the Protocycloceratidae are classified within the Ellesmerocerida because they also have concave siphuncular segments, but differ from all other ellesmeroceridans in having straight suture lines. In contrast, the Ellesmeroceratidae are confined to ellesmeroceridans with lobate suture lines. Thus, Walcottococeras Ulrich and Foerste, 1935, which has a lobate suture line and differs from the characteristic ellesmerocerid Ectenolites only in having an annulated conch, must now be assigned to the Ellesmeroceratidae. This classification agrees with Dzik (1984), who provided no explicit reason for his classification of the genus that conflicted with Flower (1964) and Sweet (1964). The latter two authors placed Walcottoceras within the Protocycloceratidae because of its annulation. Dzik (1984) erected the family Oneoceratidae to include all breviconic ellesmeroceridans. The Oneoceratidae is not accepted herein because there is no sharp differentiation between breviconic and longiconic ellesmeroceridans, and the breviconic Ellesmerocerida are likely polyphyletic, and include taxa that evolved along different lines from the longiconic Ectenolites. Genus ELLESMEROCERAS Foerste, 1921 Type species.⎯Ellesmeroceras scheii Foerste, 1921 from the Lower Ordovician at Victoria Head, Bache Peninsula, Arctic Canada. Emended diagnosis.⎯Nearly orthoconic, smooth Ellesmeroceratidae with compressed cross section and with lateral sutural lobes. Growth axis in early growth stages logarithmically curved, extends not further than apicalmost 2 cm; straight in later growth stages. Siphuncle marginal, at concave side of the shell curvature with diameter approximately one-fifth of conch cross section. Siphuncular segments concave, consist of thick connecting ring. Septal necks in some forms short and orthochoanitic, in some forms hemichoanitic to slightly loxochoanitic. Endosiphuncular diaphragms known.

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Comparison.⎯Eremoceras Hyatt, 1884 differs in being cyrtoconic in all growth stages and having a larger apical angle. Ectenolites differs in having a more slender conch and a clearly shorter, logarithmically curved juvenile conch. Occurrence.⎯Tremadocian to lower Middle Ordovician; cosmopolitan.

Discussion.⎯The emended diagnosis essentially follows Foerste (1921) and Flower (1964). However, we explicitly include no diagnosis of the shape of the conch margin in longitudinal section. In previous diagnoses of Ellesmeroceras, the conch outline is supposedly quite uniform between different species, and provides no real diagnostic features. However, we emphasize that the antisiphuncular and prosiphuncular outlines of the conch may be convex, straight, or concave, and can diverge independently from the general growth axis. In our emendation of the family, we emphasize the initially curved and subsequently straight shape of the conch as the main difference between Ellesmeroceras and all other Ellesmeroceratidae. ELLESMEROCERAS spp. Figure 5.5 Description.⎯Single specimen recovered is 32 mm long, with cross section diameter of 14 mm at adoral end, and approximately 10 mm diameter at adapical end. Growth axis and shell margins are straight; conch cross section is compressed and elliptical with small axis/large axis ratio of pproximately 0.8. Antisiphuncular side of conch is not preserved. Septal distance is 0.9 mm where the conch cross section diameter is 11 mm. (This was the only septal distance that could be measured in specimen, and probably was measured in adoral chamber of adult conch.) Siphuncle 2 mm wide where cross section diameter of conch is approximately 10 mm. Material examined.⎯One specimen, NYSM 17368, Sprakers Member, lower Tribes Hill Formation; abandoned quarry near Canajoharie (NYSM locality 6318), Montgomery County, Mohawk Valley, New York. Occurrence.⎯Only known from the Sprakers Member, lower Tribes Hill Formation in the Mohawk Valley, New York.

Discussion.⎯The nearly straight conch, the thickness of the siphuncle and the low angle of expansion of the specimen in consideration are similar to Clarkeoceras? clelandi Ulrich et al., 1943. However, it is impossible to determine the shape of the conch the poorly preserved fragment in consideration. The holotype of Clarkeoceras? clelandi has a distinctively convex antisiphuncular conch margin in longitudinal section (Ulrich et al., 1943, p. 85). The antisiphuncular conch margin is not preserved in the specimen described above, making a species determimation impossible. However, the specimen belongs to a group of species of Ellesmeroceras that rarely occur within the Tribes Hill Formation of the Mohawk Valley. Only a few specimens are known that are assigned to Orthoceras primigenium HALL, 1847 by Hall (1847), Ectenolites sp. by Ulrich et al. (1943, p. 136) and to Clarkeoceras? clelandi. Genus ANNOCERAS Flower, 1964 Type species.⎯Annoceras costatum Flower, 1964 from the Tribes Hill Formation, Washington County, New York. Diagnosis.⎯Ellesmeroceratid genus with slightly cyrtoconic conch with compressed cross section, shallow lateral sutural lobe and pronounced sutural saddle on prosiphonal side. Cross section with angular cross section margin at antisiphuncular side. Conch weakly ornamented with irregularly spaced, obliquely transverse undulations; shell thickness ca. 0.04 times cross section diameter. Siphuncle marginal on concave side of the curved shell, siphuncle diameter approximately one-fifth conch diameter but becomes proportionally smaller with respect to conch diameter with growth and toward aperture. Siphuncular segments concave, consist of thick connecting ring. Septal necks short and orthochoantic to hemichoanitic and slightly loxochoanitic. Endosiphuncular diaphragms known (diagnosis after Flower, 1964, p. 56). Occurrence.⎯The genus is known from Tribes Hill Formation in eastern New York and from Annoceras vernonense (Ulrich et al., 1943) from the Oneota Dolostone of Wisconsin.

Discussion.⎯Annoceras differs from all other Ellesmeroceratidae in having an undulated shell. Eremoceras does not have an

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FIGURE 5—Median sections of Ellesmerocerida of the Tribes Hill Formation, Early Ordovician, eastern New York; hypotype specimens unless indicated. 1, Dakeoceras mohawkense (Ulrich et al., 1943), NYSM 17336 from NYSM locality 6306, showing the orthochoanitic and relatively long septal neck, ⫻11. 2, Eorudolfoceras antiquum (Flower, 1964), NYSM 17335 from NYSM locality 5896, ⫻5.5. 3, Eorudolfoceras antiquum, NYSM 17349 from NYSM locality 5896, note the variability of the septal necks, ⫻10. 4, Clarkoceras ruedemanni Flower, 1964, NYSM 17366 from NYSM locality 5896, note the gradual transition from septa to septal necks, ⫻4.7. 5, Ellesmeroceras spp., NYSM 17368 from NYSM locality 6318, the median section shows only a fragment of the conch width, note the wide siphuncle, ⫻3.8. 6, Ectenolites extensus Flower, 1964, paratype NYSM 17339 from NYSM locality 5896, note the gradual thickening of the shell at aperture, ⫻6.9. 7, Dakeoceras champlainense n. sp., paratype NYSM 17363 from NYSM locality 5927, with achoanitic septal necks, ⫻11. 8, Annoceras costatum Flower, 1964, NYSM 17369 from NYSM locality 5898, ⫻14. 9, Dakeoceras champlainense n. sp., holotype NYSM 17312 from NYSM locality 5898, with achoanitic septal necks, ⫻8.

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO undulated shell, has a shallower sutural saddle on the prosiphuncular side, and lacks the angular cross section margin. ANNOCERAS COSTATUM Flower, 1964 Figures 5.8, 6.2–6.8, 7.2, 7.3 Annoceras elevatum FLOWER, 1964, p. 57, pl. 6, figs. 11, 16; WOLBERG, 1990b, p. 854. Annoceras perobliquum FLOWER, 1964, p. 57, pl. 6, fig. 11; pl. 12, figs. 6, 7; WOLBERG, 1990b, p. 854. Annoceras costatum FLOWER, 1964, p. 56, 57, pl. 6, figs. 10, 17, 18; pl. 7, figs. 19, 20, 23. Ellesmeroceras angulatum FLOWER, 1964, p. 48, pl. 6, figs. 3, 4; WOLBERG, 1990b, p. 853. Ellesmeroceras fusiforme FLOWER, 1964, p. 47, pl. 6, figs. 14, 15; WOLBERG, 1990b, p. 854. Ellesmeroceras imbricatum FLOWER, 1964, p. 47, pl. 7, fig. 13; WOLBERG, 1990b, p. 853. Ellesmeroceras indomitum FLOWER, 1964, p. 47, pl. 6, fig. 13; pl. 7, figs. 21, 22; WOLBERG, 1990b, p. 853. Ellesmeroceras progessum FLOWER, 1964, p. 47, pl. 6, figs. 5–7; DZIK, 1984, p. 20, fig. 2. 21; WOLBERG, 1990b, p. 853. Eremoceras magnum FLOWER, 1964, p. 51, pl. 10, fig. 1; pl. 25, fig. 1; WOLBERG, 1990b, p. 854. Eremoceras (?) sp. cf. magnum FLOWER, 1964, p. 47, pl. 6, fig. 13; pl. 7, figs. 21, 22. Eremoceras perseptatum FLOWER, 1964, p. 50, pl. 6, figs. 8, 9; WOLBERG, 1990b, p. 854. Eremoceras progressum (Flower). DZIK, 1984, p. 20.

Diagnosis.⎯Annoceras species with apical angle that changes during ontogeny; apical angle ca. 14⬚ in early growth stages and ca. 6⬚ in latest growth stages. Slightly cyrtoconic conch with nearly straight margin on concave side of growth axis, and convex margin on convex side of growth axis. Conch cross section compressed with angular or rounded margin on concave side of growth axis. Pro-, and antisiphuncular sections of lateral sides of conch flattened to a varying degree between specimens. Shell has oblique undulations that slope toward the aperture on antisiphuncular side of conch. Sutures have high, distinct saddles on prosiphuncular side of the conch and lateral lobes. Saddle height variable between specimens, and equals the distance between three to five septa; low, inconspicuous saddle on antisiphuncular side of conch (diagnosis after Flower, 1964). Description.⎯Growth axis slightly cyrtoconic; in some cases, growth axis is slightly S-shaped in later growth stages. Siphuncle is at concave side when referring to the entire length of conch. Prosiphuncular conch margin in lateral section is straight or slightly convex in later growth stages. Therefore siphuncle is on convex side of conch in fragments with cross section diameter greater than 20 mm. However, some specimens have straight mature shell (Fig. 6.6) or a shell entirely bent in one direction with siphuncle at concave side of growth axis (Fig. 6.2). All transitions between these different morphologies exist in the NYSM collection. Cross section compressed and elliptical; early growth stages generally more rounded with short axis/long axis ratio of 0.9, later growth stages more compressed and ratio ranges from 0.73, specimen NYSM 17312, to 0.9, specimen NYSM 17320. Cross section has angular margin at antisiphuncular side in some specimens and at prosiphuncular in all specimens. Antisiphuncular margin of cross section is always more rounded compared with prosiphuncular margin, degree of flattening of lateral sides of conch and development of prosiphuncular angular margin varies between specimens (Fig. 7.2, 7.3). All of these morphological transitions are known to occur in different specimens. Apical angle of early growth stages (at cross section diameter approximately 15 mm) 15–17⬚. Largest known specimen with long cross section axis length of 28 mm (specimen NYSM 17320). One adult specimen has long cross section axis length of 27 mm. However, other specimens known from large phragmocones indicate a larger adult size. Outer shell 0.88 mm thick at cross section diameter of 22 mm in specimen NYSM 17322. Shell has undulations of varying height, with undulations increasing in height during ontogeny and with highest undulations near aperture (Fig. 6.7, 6.8). Interspecimen variation ranges from sharply defined to very shallow and widely spaced undulations. Undulations slope obliquely and toward aperture on antisiphuncular side. Septal spacing narrow, length of 16 chambers approximately equivalent to cross section length (this range extends from a maximum of 18 chambers, specimen NYSM 17327, to a minimum of 12 chambers, specimen NYSM 17317). Curvature of septa is low. Sutures form shallow, broad saddle on antisiphuncular side, wide and shallow lateral lobe, and a pronounced saddle

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on prosiphuncular side. Sutural saddle at prosiphuncular side has height similar to distance of three to four septa. Siphuncle marginal, measures ca. 0.3 times cross section diameter (specimen NYSM 17324). Shape of septal necks and siphuncular segments not examined.

Comparison.⎯Annoceras multicameratum Flower, 1964 differs by having a conch with a different expansion rate during ontogeny and a smaller adult size. Material examined.⎯Hundred and twenty seven specimens from the NYSM Paleontology Collection from NYSM localities TRQ-32, 5896, 5927, 6311, 6326, 6328. Occurrence.⎯Only known from the Wolf Hollow and Canyon Road Members, Tribes Hill Formation; Herkimer, Montgomery, and Washington counties in the Lake Champlain lowlands and Mohawk River valley, eastern New York.

Discussion.⎯The name Annoceras costatum is misleading, because the conch is not costate, but undulated. In A. costatum, two types of variability are evident. The first is variation in cross section. The cross section in some specimens is strongly compressed and in others nearly circular (compare Fig. 6.3, 6.4). As a rule, the strongly compressed specimens have an angular prosiphuncular conch margin and a higher sutural saddle, the less compressed have a more rounded margin and a shallower sutural saddle. The angular conch margin always occurs in specimens with flattened conch margins at antisiphuncular sections of laterals side, which vary in length with cross section compression. In more compressed shells, the flattened sides are longer than in more rounded ones. Specimens representing all transitions are in the NYSM collections. In the second type of variation, the amplitude and spacing of the shell undulation differs strongly between specimens. All transitions between nearly smooth specimens and strongly undulose specimens occur in the NYSM collection. These completely gradational variations in conch cross section and surface topography emphasize that it is impossible to use these features, as did Flower (1964), to establish a number of Annoceras and Ellesmeroceras species (see species synonymy, above). Because Annoceras perobliquum is based on the shape and spacing of undulation and A. elevatum is based on the high sutural saddle, these species are herein synonymized with A. costatum. Flower (1964) assigned some very slightly undulated conchs, which are otherwise similar to A. undulatum Flower, 1964 to new Ellesmeroceras species, and these are also brought into synonymy. Indeed, Flower’s (1964) genus classification also is not useful, because all of the Smith Basin species that he assigned to Ellesmeroceras are cyrtoconic. The diagnostic character of E. angulatum and Eremoceras progressum, which are nearly smooth but otherwise similar to the type of A. costatum, is the degree of flattening of the lateral conch sides at the prosiphuncular margin. Both species are herein regarded as nearly smooth variants of A. costatum. The difference between the types of Ellesmeroceras indomitum and E. progressum involves only minimal differences in apical angle. Therefore, E. indomitum is also synonymized with A. costatum. Ellesmeroceras fusiforme is based on a single adult specimen that strongly resembles specimen NYSM 17327, which is an adult A. costatum conch with shallow undulation and rounded cross section. Similarly, Ellesmeroceras imbricatum is an exfoliated A. costatum conch. Eremoceras magnum, which is known only from the type, differs from A. costatum only by its relatively large size, and is also synonymized with A. costatum. Eremoceras perseptatum, based on a single sectioned specimen, is only an oblique median section of an A. costatum conch. ANNOCERAS

MULTICAMERATUM

(Flower, 1964)

Figure 7.1, 7.4 Eremoceras multicameratum FLOWER, 1964, p. 50, pl. 6, figs. 1, 2, pl. 10, fig. 14, pl. 28, fig. 7; WOLBERG, 1990b, p. 853.

Emended diagnosis.⎯Annoceras species with conchs that have a large apical angle (ca. 26⬚) in earlier growth stages, a low apical

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FIGURE 6—Ellesmerocerida of the Tribes Hill Formation, Early Ordovician, eastern New York; hypotype specimens. 1, Eremoceras teres Ulrich et al., 1943, NYSM 17310 from NYSM locality 5927, note the short body chamber, ⫻ 2.2. 2–8, Annoceras costatum; 2, 3, NYSM 17353 from NYSM locality 5896, specimen with strong curvature and strongly compressed cross section, lateral view and view from the antisiphuncular, convex side, ⫻1.6; 4, NYSM 17309 from NYSM locality TRQ-32, specimen with a nearly circular cross section, ⫻2; 5, NYSM 17307, from 5898, note the longitudinal striae on the mold and the imbricated shell fragments, ⫻2.5; 6–8, NYSM 17320 from NYSM locality 5896, specimen with gentle conch curvature, wide expansion rate, and wide cross section, note the undulated shell and the longitudinal striae on the mold of the body chamber, left-lateral view, view from prosiphuncular, straight side, and right-lateral view, respectively, ⫻1.7.

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO

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FIGURE 7—Ellesmerocerida of the Tribes Hill Formation, Early Ordovician, eastern New York; hypotype specimens. 1, Annoceras multicameratum (Flower, 1964), NYSM 17321 from NYSM locality 5927, antispihuncular side, note the characteristic decrease of the apical angle along growth direction, ⫻2. 2, 3, Annoceras costatum (Flower, 1964), view of the sutural saddles on anitisphuncular side, compare the variation of saddle height and shape; 2, NYSM 17319 from NYSM locality 5927, ⫻2.4; 3, NYSM 17308 from NYSM locality 5927, ⫻2.7. 4, Annoceras multicameratum, NYSM 17317 from NYSM locality 5896, lateral view, note the characteristic shape of the adult aperture, ⫻2.2. 5, Dakeoceras harrisi Flower, 1964, NYSM 17370 from NYSM locality 6296, section along the longitudinal axis, note the strong dolomitization, ⫻2. 6, 7, Eorudolfoceras antiquum, NYSM 17373 from NYSM locality 5896, ⫻1.8; 6, lateral view, note the long body chamber and the slightly oblique sutures. 7, prosiphuncular, convex side, note the asymmetric arrangement of the undulation. 8, Eorudolfoceras praenuntium (Flower, 1964), NYSM 17345 from NYSM locality 5896, lateral view, note the strongly oblique sutures, ⫻1.3. 9, 10, Eorudolfoceras antiquum, from NYSM locality 5927; 9, NYSM 17346, nearly adult specimen, prosiphuncular, convex side, this is a view exactly along the symmetry axis of the conch, note the strongly oblique, asymmetric undulation, ⫻1.6; 10, NYSM 17348, juvenile specimen, view approximately along convex side, note the thick shell, ⫻4.8.

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angle in later adolescence, and a slight constriction of the conch in adult sizes. Conch slightly cyrtocone with prosiphuncular margin less convex than antisiphuncular side. Cross section compressed with angular margin on prosiphuncular side. Lateral sides of conch are slightly flattened on prosiphuncular side. Shell has very shallow undulations that are more distinct adorally. Septal spacing is narrow, with ca. 16 chambers along a length comparable to cross section diameter. Sutures with high, well-marked saddle on prosiphuncular side of the conch and with lateral lobes. Low inconspicious saddle at antisiphuncular side of conch. Description.⎯Growth axis slightly cyrtoconic, siphuncle on concave side. Antisiphucular margin of conch convex throughout length. Prosiphuncular margin concave until cross section diameter of ca. 17 mm is reached, then convex in later growth stages; this reversal in convexity produces a fusiform conch shape in adult specimens (Fig. 7.4). Apical angle ca. 26⬚ at 12–18 mm distance from apex, ca. 6⬚ at 19–21 mm (specimen NYSM 17318). Cross section is compressed ellipse; early growth stages generally more rounded, with short axis/long axis ratio of 0.9 in 10 mm diameter conch; later growth stages more compressed, with short axis/long axis ratio of 0.83 in 21 mm diameter conch (specimen NYSM 17318). Prosiphuncular side of cross section is angular, antisiphuncular side rounded. Largest known specimen has long cross section axis length of 21 mm (specimen NYSM 17318). Surface of adult conch has undulations that vary in height along conch and between specimens. Undulations slope slightly obliquely toward aperture on antisiphuncular side. Septal spacing is narrow, approximately 15–16 chambers over a distance comparable to cross section diameter. Curvature of septa low. Sutures form shallow, broadly rounded saddle on antisiphuncular side; subtle, wide, and shallow lateral lobe and pronounced saddle on prosiphuncular side. Sutural saddle on prosiphuncular side with height similar to length of three chambers.

Comparison.⎯Annoceras costatum differs in having a more constant expansion rate during growth and a larger adult size. The sutural saddle height is generally lower than in Annoceras costatum, and equals distance spanned by two to three septa. Material examined.⎯Five specimens in the NYSM Paleontology Collection; NYSM localities 5896 and 5927 from Washington County in the Lake Champlain lowlands, eastern New York. Occurrence.⎯The species is known only from the Wolf Hollow and Canyon Road members, upper Tribes Hill Formation, in Washington County, eastern New York.

Discussion.⎯Flower (1964) named the species for its numerous septae and camerae, and emphasized a close septal spacing. However, the NYSM specimens show that there is no conspicuous difference between the septal spacing in Annoceras costatum and A. multicameratum. Both species have approximately 16 chambers along a distance comparable to the cross section diameter. Flower (1964) assigned both of the latter species to Eremoceras Hyatt, 1884. However, the additional NYSM material reveals a slightly undulatory shell and an angular margin along the prosiphonal side of the cross section, which are diagnostic features of Annoceras. The siphuncular and septal neck shapes were not observable in the NYSM specimens. However, Flower (1964, p. 50) described a round siphuncular cross section, endosiphuncular diaphragms, and short septal necks in Annoceras multicameratum. Genus CLARKOCERAS Ruedemann, 1905 Type species.⎯Piloceras newton-winchelli Clarke, 1897, from the Oneota Dolostone of Houston County, Minnesota. Diagnosis.⎯Ellesmeroceratids with somewhat cyrtoconic conch with strongly compressed cross section showing large apical angle in lateral view and small apical angle in vertical view; aperture and sutures slope obliquely toward the convex side of the conch; sutures with very shallow lateral lobes, nearly straight in some species. Siphuncle marginal or slightly displaced from concave margin of conch, typically ovate in cross section; siphuncular segments concave, consist of thick connecting ring; septal necks are variably achoanitic, orthochoanitic, or hemichoanitic; endosiphuncular diaphragms known (diagnosis after Flower, 1964, p. 67). Occurrence.⎯Lower Lower Ordovician; cosmopolitan.

Comparison.⎯Levisoceras Foerste, 1925 and Dakeoceras Ulrich and Foerste, 1931 differ in having a stronger conch curvature and a higher apical angle. Eremoceras differs in lacking the strong differentiation between lateral and vertical apical angles and in having generally less oblique sutures. CLARKOCERAS

RUEDEMANNI

Flower, 1964

Figure 5.4 Clarkeoceras ruedemanni FLOWER, 1964, p. 69, pl. 10, figs. 2; WOLBERG, 1990b, p. 854.

Emended diagnosis.⎯Clarkoceras species with moderately flexed, strongly compressed conch, moderate vertical expansion angle of 20⬚; conch cross section elliptical with rounded margins and ratio short axis/long axis ratio of 0.6–0.7. Sutures essentially transverse with very shallow lateral lobes. Siphuncle marginal on concave side of conch, measures ca. 0.3 times vertical cross section diameter, with concave segments. Septal necks short and orthochoanitic to hemicoanitic. Description.⎯Curvature of conch moderate, concave margin with very broad curvature, convex margin more narrowly curved. Cross section laterally compressed ellipse with rounded margins, thus the cross section of specimen NYSM 17364 has 35 mm-long vertical axis and a shorter, 17 mm long lateral axis. Ca. 20⬚ vertical apical angle means length of vertical cross section increases from 17 mm to 35 mm along 47 mm of conch NYSM 17364. Lateral apical angle of ca. 15⬚ means length of cross section increases from 15 mm to 19 mm along 19 mm of conch NYSM 17365. Septa slope very slightly, less than 5⬚, toward convex side of conch. Septal distance 1.7 mm where diameter of specimen NYSM 17364 is 35 mm. Sutures form very shallow lateral saddles. Siphuncle with concave segments; septal necks in specimen NYSM 173566 are hemichoanitic, measure approximately half of chamber distance, and have gradual curvature (Fig. 5.4).

Comparison.⎯Clarkoceras ruedemanni differs from all other species of the genus in combining a strongly compressed conch with moderate vertical expansion rates. Clarkoceras crassum Ulrich et al., 1943 differs in having a wider conch cross section. Clarkoceras luthei (Calvin, 1892) differs in having a lower expansion rate and a wider cross section. Material examined.⎯Forty specimens in the NYSM collection; all from the Wolf Hollow and Canyon Road members, upper Tribes Hill Formation; NYSM localities 5896 and 5927, Washington County, Lake Champlain lowland, eastern New York. Occurrence.⎯Only known from the upper Tribes Hill Formation, Washington County, eastern New York.

Discussion.⎯The diagnosis generally follows Flower’s (1964, p. 67). The additional material in the NYSM collection revealed more precise data on cross section diameter and internal characters. These data are incorporated in the diagnosis. They show that the curvature of the septal necks in Clarkeoceras ruedemanni is gradual and differs from that in typical orthochoanites. Genus DAKEOCERAS Ulrich and Foerste, 1931 Type species.⎯Dakeoceras normale Ulrich and Foerste, 1931, from the Van Buren Formation, Washington County, Missouri. Diagnosis.⎯Ellesmeroceratids with a slightly cyrtoconic conch with growth axis that progressively straightens with growth; conch cross section is moderately laterally compressed; siphuncle marginal on concave side of conch; siphuncular segments concave, consist of a thick connecting ring; septal necks are variably achoanitic, orthochoanitic, or hemichoanitic; sutures transverse (diagnosis after Flower, 1964, p. 61). Occurrence.⎯Lower Lower Ordovician; North America, China.

Discussion.⎯The apical angle of the Dakeoceras conch is moderate compared with that of other ellesmeroceratid genera. The genus is similar to Eremoceras in general shell shape, but differs in having nearly straight sutures. Levisoceras and Conocerina Ulrich and Foerste, 1931 differ in having a stronger conch curvature and a higher apical angle. DAKEOCERAS CHAMPLAINENSE new species Figures 5.7, 5.9, 8.8–8.11 Diagnosis.⎯Dakeoceras species with conch with very gentle curvature; conch cross section oval, slightly laterally compressed;

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO apical angle ca. 15⬚, adult cross section diameter more than 17 mm; approximately 10 chambers occur along a length comparable to the cross section diameter; sutures have very shallow saddle on prosiphuncular side of conch. Description.⎯Conch faintly ornamented with very fine transverse striae (Fig. 8.8). Conch wall 0.52 mm thick where specimen NYSM 17312 measures 16 mm in diameter (⫽0.053 times cross section diameter) and 0.36 mm thick where specimen NYSM 17308 measures 14 mm in diameter. Apical angle of conch fragments ranges from 13⬚ in specimen NYSM 17312 to 17⬚ in specimen NYSM 17316. Septal spacing narrow, with average of 10 chambers in a distance comparable to the cross section diameter (a range of 9–11 chambers in a distance comparable to the cross section diameter was measured in seven specimens). Suture forms shallow lateral lobes and saddle on antispihuncular side of conch with height of lobes and depth of saddles comparable to the distance spanned by two chambers. Siphuncle thickness ca. 0.2 times cross section diameter (e.g., 2 mm thick where conch cross section diameter is 12 mm in specimen NYSM 17315). Septal necks achoanitic (specimen NYSM 17313, 17314, Fig. 5.7, 5.9). Specimen NYSM 17308 has shallow longitudinal ridges on mold of inner surface of shell. Etymology.⎯Champlainense (L.); the species was first recognized in the southern Lake Champlain lowlands of eastern New York. Types.⎯Holotype NYSM 17316 and paratypes NYSM 17306–17308, 17311–17316, and NYSM 17363 from NYSM localities 5896, 5898, and 5927 in the upper Tribes Hill Formation, Washington County, New York. Occurrence.⎯The species is known only from the Wolf Hollow and Canyon Road Members of the Tribes Hill Formation in the southern Lake Champlain lowlands, Washington County, eastern New York.

Discussion.⎯Dakeoceras champlainense new species is unique within the genus in having a very gentle curvature of the conch. DAKEOCERAS HARRISI Flower, 1964 Figure 7.5 Clarkoceras? clelandi ULRICH, E. O., A. F. FOERSTE, AND A. MILLER., 1943, p. 85, pl. 45, figs. 12. Clarkeoceras clelandi, FLOWER, 1964, p. 62. Dakeoceras harrisi FLOWER, 1964, p. 62, pl. 8, figs. 8, 13, 14; WOLBERG, 1990b, p. 854.

Diagnosis.⎯Dakeoceras species with slender comparatively strongly curved conch; conch cross section elliptical with rounded margins and short axis/long axis ratio of 0.8. Apical angle of conch less than 10⬚. Sutures are essentially transverse and have very shallow lateral lobes. Siphuncle marginal, on concave side of conch, measures ca. 0.3 times vertical cross section diameter, and has concave segments. Septal necks orthochoanitic (diagnosis after Flower, 1964, p. 62). Description.⎯The only specimen recovered in this study (NYSM 17362) is an approximately 35 mm long, strongly bent conch fragment that expands aperturally from 7 mm to 12 mm. Septa are essentially straight, transverse, and separated by distance of ca. 1 mm at apertural end of fragment. Siphuncle marginal on concave margin of conch, 3 mm diameter at apertural end. Connecting ring thick, with concave segments. Material examined.⎯One specimen in the NYSM collection; lower Canyon Road Member, upper Tribes Hill Formation; NYSM locality 6296, Montgomery County, Mohawk River valley, eastern New York. Occurrence.⎯The type material described by Flower (1964) was collected along the Erie Canal just east of Fort Hunter, Montgomery County, New York, in beds of the upper Tribes Hill Formation. The specimen described by Ulrich et al. (1943, p. 85) was collected about 40 km west of Fort Hunter from Cleland’s (1900) horizon II-3. Thus, the species is presently only known from the lower Canyon Road Member, Tribes Hill Formation, in the Mohawk River valley, eastern New York.

Discussion and comparison.⎯The preservation of the available specimen is poor as a result of dolomitization. Despite this, it represents the most nearly complete fragment known from Dakeoceras harrisi, and the general conch shape is now much better known. The combination of a slender conch and its comparatively strong curvature are unique to Dakeoceras harrisi and distinguish it from other species of the genus. The paratype of Clarkeoceras? clelandi is brought into synonymy because it displays the characteristic features of D. harrisi. DAKEOCERAS GRACILIS (Cleland, 1903) Figures 8.6, 8.7 Cyrtoceras sp. CLELAND, 1900, p. 19, pl. 17, figs. 5, 6.

Cyrtoceras gracile CLELAND, 1903, p. 13, pl. 3, figs. 11. Ectenoceras? gracile (CLELAND). ULRICH, E. O., A. F. FOERSTE, MILLER., 1943, p. 121, pl. 57, figs. 26, 27. Ectenolites gracilis (CLELAND). FLOWER, 1964, p. 53.

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AND

A.

Diagnosis.⎯Dakeoceras species with small, slender conch with long body chamber and low apical angle (ca. 6⬚). Cross section strongly compressed oval with slightly angular margin along concave side of shell. Adult cross section diameter of 9 mm. Seven to ten chambers occur in a length comparable to cross section diameter. Sutures form very shallow saddle on prosiphuncular side of conch and shallow lateral lobes. Siphuncle narrow with diameter ca. 0.1 times conch cross section diameter. Description.⎯Shell curved, expands from 7.3 mm to 9 mm (long axis of cross section) along 21.5 mm long conch (NYSM 17346) and from 7 mm to 9 mm along a second, 21 mm long conch (NYSM 317345). NYSM 17346 is an adult specimen with ca. 8 mm long body chamber that shows narrowing at aperture. Cross section strongly elliptical with slightly narrower margin on concave side of conch. Sutures have relatively uniform spacing of ca. 0.6 mm, which results in septal spacing of ca. 8 septa in a length comparable to the cross section diameter in apical parts of conch, and 10 septa in apertural parts. Specimen NYSM 17336 has two chambers and a fragmentary bod chamber with 4.5 mm length. Elliptical cross section has 6.3 mm long axis, and 4.5 mm short axis. Sutures have shallow lateral lobes. Two chambers have 0.6 mm and 0.7 mm depths. Siphuncle displaced 0.3 mm from concave margin conch. Siphuncular tube with concave segments and 0.7 mm diameter. Material examined.⎯Three specimens (NYSM 17336, 17345, and 17346) from NYSM localities 6306, 6308, 6310 in the lower Canyon Road Member, upper Tribes Hill Formation, Montgomery County, Mohawk River valley, eastern New York. Occurrence.⎯The species is presently known only from the lower Canyon Road of the upper Tribes Hill Formation, Mohawk River valley, eastern New York.

Discussion and comparison.⎯Previously, the species was known only from internal phosphatic molds of the body chamber and adjacent parts of septate conchs that are rare in the upper Tribes Hill Formation of the Mohawk River valley (i.e., lower Canyon Road Member, or ‘‘Fonda Member’’ of Fisher, 1954). The discovery of two specimens with preserved parts of the phragmocone now clearly shows the trend of the growth axis and the apical angle of the shell, and thus has allowed reassignment of this species to Dakeoceras. The new data show that D. gracilis is a small, slender species that is unique within the genus, combining a long body chamber and low apical angle. It differs from species of Ectenolites in having a curved conch with higher extension rate. Genus ECTENOLITES Ulrich and Foerste, 1935 Type species.⎯Ectenolites subgracilis Ulrich and Foerste, 1935, from the Gasconade Dolostone, Franklin County, Missouri. Diagnosis.⎯Ellesmeroceratids with slender conch with compressed cross section and lateral sutural lobes. Logarithmically curved juvenile growth axis straightens within 5 mm of apex; angle of expansion very low, less than 5⬚. Conch gently curved along lower third or half of length and nearly straight along middle and lower parts. Conch smaller than in most longiconic Ellesmerocerida, with adult length usually less than 50 mm. Outer shell is smooth. Siphuncle marginal or slightly displaced from margin on concave side of shell or at convex side in some forms. Siphuncular segments concave, consist of thick connecting ring; septal necks short and orthochoanitic or achoanitic. Endosiphuncular diaphragms known. Occurrence.⎯Uppermost Cambrian–Lower Ordovician; North America, Greenland, North China.

Discussion.⎯The diagnosis of the species in consideration largely follows Ulrich and Foerste (1935, p. 272), and Flower (1964, p. 52). The growth axis in the juvenile parts of Ectenolites conchs is always nearly straight adorally of 5 mm from tip, as the logarithmically curved juvenile growth axis of Ellesmeroceras straightens about 10 mm from the apex. Bassleroceras Ulrich and Foerste, 1935 differs in having a larger and less slender conch that is conspicuously cyrtoconic throughout entire length and in

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FIGURE 8—Ellesmerocerida of the Tribes Hill Formation, Early Ordovician, eastern New York; hypotypes unless indicated. 1, 2, Ectenolites sinuatus Flower, 1964, from NYSM locality 5927; 1, NYSM 17326, lateral view of juvenile specimen, note the smooth shell and the nearly straight conch, ⫻2.6; 2, NYSM 17340, lateral view, note the long body chamber, the oblique sutures, and the longitudinal furrows on the mold of the body chamber, ⫻2.5. 3–5, Ectenolites clelandi (Ulrich et al., 1944). 3, NYSM 17334 from NYSM locality 5896, note the long body chamber and the nearly straight sutures with deep lateral saddles, ⫻2.5; 4, NYSM 17329 from NYSM locality 5896, note the longitudinal striae on the mold of the body chamber, ⫻2.3; 5, NYSM 17327 from NYSM locality 5927, specimen shows the slightly bent growth axis, ⫻1.7; 6, 7, Dakeoceras mohawkense (Ulrich et al., 1943). 6, NYSM 17372 from NYSM locality 6310, note the short body chamber, the oblique sutures, and the longitudinal striae at the mold of the body chamber, ⫻2.9; 7, NYSM 17371, from NYSM locality 6308, note the longitudinal striae at the mold, ⫻3.8; 8–11, Dakeoceras champlainense n. sp.; 8, paratype NYSM 17315 from NYSM locality 5896, detail of the ornamentation, same specimen as in 8, ⫻6; 9, paratype NYSM 17306 from NYSM 5927, silicified mold, showing the shape of chambers

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO having a smaller siphuncular diameter. Walcottoceras and Rudolfoceras, and Eorudolfoceras differ in having an annulated shell. ECTENOLITES CLELANDI Ulrich, Foerste, Miller, and Unklesbay, 1944 Figure 8.3–8.5 Cyrtoceras kirbyi? CLELAND, 1900, p. 259, pl. 17, figs. 3, 4. Bassleroceras clelandi ULRICH, FOERSTE, MILLER, AND UNKLESBAY, 1944, p. 36, pl. 7, figs. 7, 8. Ectenolites penecilin FLOWER, 1964, p. 46, 50, 55, pl. 7, figs. 10–12; CHEN AND QI, 1981, p. 138, pl. 1, figs. 10; WOLBERG, 1990b, p. 854. Ellesmeroceras penecilin (FLOWER). DZIK, 1984, p. 20.

Diagnosis.⎯Ectenolites species with relatively strongly compressed cross section of conch, and slightly oblique sutures that slope toward aperture on concave side of conch; sutures form broad rounded lateral lobes with highest amplitude on convex side of conch. Conch cross section elliptical without angular margin on concave or convex side. Siphuncle marginal, has concave segments; septal necks very short, orthochoanitic (diagnosis after Flower, 1964, p. 56). Description.⎯Conch slightly bent with elliptical cross section. Cross section margin on prosipuncular side (i.e., on concave side of growth axis and conch) slightly more narrowly rounded than that on opposite side. Maximum cross section diameter 9 mm (specimen NYSM 17329) with short axis/long axis ratio of 0.72. Conch wall smooth, thin, with thickness of 0.28 mm (⫽0.07 times cross section diameter) where specimen NYSM 17338 has a cross section diameter of 4 mm. Body chamber has maximum length of 18 mm and maximum 9 mm diameter in specimen NYSM 17328; longitudinal furrows occur on mold of body chamber of specimen NYSM 17329 (Fig. 8.4). Approximately seven chambers occur over length comparable to cross section diameter. Material examined.⎯Four specimens from Wolf Hollow and Canyon Road Members, upper Tribes Hill Formation; NYSM localities 5927 and 5896, Washington County, Lake Champlain lowland, eastern New York. Occurrence.⎯Uppermost Cambrian–Tremadocian, Early Ordovician; Zhejiang Province, South China; New York, Vermont.

Discussion.⎯The absence of an angular margin on the concave and convex sides of the conch of Ectenolites clelandi differs from that of Ectenolites longus (Ulrich et al., 1943). Ectenolites clelandi differs from Eectenolites compressum (Ulrich et al., 1943) in having a comparatively long body chamber with a length/cross section ratio of more than 2.5. ECTENOLITES

EXTENSUS

Flower, 1964

Figure 5.6 Ectenolites extensus FLOWER, 1964, p. 55, pl. 7, figs. 1–6; WOLBERG, 1990b, p. 854.

Emended diagnosis.⎯Ectenolites species with oblique sutures sloping toward aperture along concave side of conch. Sutures form broad rounded lateral lobes. Camerae closely spaced, with approximately eight septa occurring in a length comparable to cross section diameter. Conch cross section compressed, with low apical angle and comparatively rounded cross section. Siphuncle with concave segments, diameter ca. 0.2–0.3 times conch diameter. Body chamber comparatively long, with length/cross section ratio ⬎ 2.0. Description.⎯Specimen NYSM 17332 is 29 mm long, with maximum cross section diameter of 7.3 mm and 5.5 mm diameter at adapical end. Growth axis slightly bent. Cross section of conch is elliptical with short axis/ long axis ratio of 0.72 at apical end. Outer shell smooth, but not preserved. Approximately eight chambers occur over a length comparable to cross section diameter. Sutures oblique and slope ca. 30⬚ perpendicular apically on convex side of conch. Length of body chamber ca. 17 mm. Specimen NYSM 17339 is 33 mm long, with 8 mm maximum cross section diameter and minimum cross section diameter of 3.5 mm. Length of eight chambers is approximately comparable to conch diameter. Siphuncle marginal

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on convex side of conch, with diameter of 20% of cross section diameter and concave segments. Septal necks short.

Comparison.⎯Ectenolites extensus differs from all other species of the genus in having a comparatively rounded cross section. Material examined.⎯Two specimens NYSM 17332, 17339, Wolf Hollow and Canyon Road members, Tribes Hill Formation; hilltop north of Rte. 22 and east of Comstock, NYSM localities 5927, 5896, Washington County, Lake Champlain lowland, New York. Occurrence.⎯Lower Ordovician Chepultapec Limestone in Virginia and upper Tribes Hill Formation, New York.

Discussion.⎯The emended species diagnosis generally follows Flower (1964, p. 55). We emend the diagnosis in order to include the characters of the siphuncle, which are informative in the Ellesmeroceratidae. Flower (1964, p. 55) indicated a relatively wide siphuncle with a diameter equivalent to 0.26 times the cross section diameter of the conch. Although the siphuncle that we prepared from the NYSM collection has a diameter of only 0.2 times that of the conch, we regard this difference as minor, and emphasize the characteristic siphuncle position and suture shape as more diagnostic of the species. ECTENOLITES SINUATUS Flower, 1964 Figure 8.1, 8.2 Ectenolites sinuatus FLOWER, 1964, p. 56, pl. 7, fig. 7; WOLBERG, 1990b, p. 854. Ectenolites simplex FLOWER, 1964, p. 56, pl. 7, fig. 9; WOLBERG, 1990b, p. 854.

Emended diagnosis.⎯Ectenolites species with slender, relatively smooth conch is moderately compressed with inclined septa that slope toward aperture on concave side of conch. Cross section is compressed elliptical with short axis/long axis ratio of more than 0.8. Sutures form marked rounded saddle on concave (prosiphuncular) side of conch, and broadly rounded lateral lobes. Siphuncle marginal, on concave side of conch. Body chamber length/cross section ratio of more than 2.0. Description.⎯Of seven specimens examined, the conch of NYSM 17340 has the greatest cross section diameter (8.2 mm). Its elliptical cross section has a short axis/long axis ratio of 0.76, while specimen NYSM 17344 has a 0.8 ratio 4.5 mm from apex. Conch is nearly straight even in juvenile growth stages with diameter less than 4 mm. Sutures form broad rounded lateral lobes and conspicuous saddle on the concave side of conch. Approximately seven chambers occur over length comparable to cross section diameter. Outer shell of conch generally smooth; faint growth lines with spacing of ca. 0.25 mm were noted on specimen NYSM 17344 where the conch cross section diameter is 5 mm. Shell thickness 0.35 mm (⫽ 0.07 times cross section) in specimen NYSM 17343 where conch cross section diameter is 5 mm. Body chamber of specimen NYSM 17344 has maximum cross section diameter of 6 mm and 12 mm length.

Comparison.⎯Ectenolites sinuatus differs from other species of the genus by the presence on the conch of deep lateral lobes which are less inclined to the growth axis and conch. The otherwise similar E. pergracilis (Ulrich et al., 1943) differs in having lateral lobes with centers that are excentric on the convex side of the conch. Material examined.⎯Seven specimens from the Wolf Hollow and Canyon Road members, upper Tribes Hill Formation; NYSM localities 5927 and 5896, Washington County, Lake Champlain lowland, New York. Occurrence.⎯Species only known from the upper Tribes Hill Formation, eastern New York.

Discussion.⎯The emended diagnosis of Ectenolites sinuatus generally follows Flower’s (1964, p. 56). We included the presence of a smooth shell within the diagnosis. Ectenolites simplex is regarded as a junior synonym because it was erected on the basis of only one smooth conch that is otherwise similar to that of E. sinuatus. Our study suggests that a smooth shell is probably a character of many Ectenolites species, including E. sinuatus.

← and position and shape of siphuncle, ⫻3; 10, same specimen as in 8, note the shape of the body chamber and thickness of shell, ⫻3; 11, paratype NYSM 17314 from NYSM locality 5896, view approximately along antisiphuncular, concave side, showing a shallow sutural saddle and faint longitudinal striae at the mold, ⫻3.2.

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JOURNAL OF PALEONTOLOGY, V. 81, NO. 5, 2007 Genus EORUDOLFOCERAS new genus

Type species.⎯Rudolfoceras antiquum Flower, 1964, from Tribes Hill Formation, Tremadocian, Smith Basin, Washington County, New York. Included species.⎯Rudolfoceras antiquum Flower, 1964, Rudolfoceras prenuntium Flower, 1964. Diagnosis.⎯Ellesmeroceratids with slender, annulated, slightly cyrtoconic conch with shallow lateral sutural lobe. Logarithmically curved juvenile growth axis straightens within 5 mm of apex; apical angle is very low, less than 7⬚. Siphuncle marginal, or slightly displaced from convex side of the shell, approximately 0.3 of conch cross section in diameter. Connecting ring thin, siphuncular segments concave; septal necks short and orthochoanitic or achoanitic; endosiphuncular diaphragms not known. Etymology.⎯From Latin, for early, referring to the stratigraphically older occurrence of the genus in consideration compared with the similar Rudolfoceras Ulrich et al., 1944. Occurrence.⎯Tribes Hill Formation, Tremadocian; New York, North America.

Discussion.⎯Rudolfoceras differs in having a higher angle of expansion and a siphuncle that is approximately 0.1 of conch cross section in diameter. Ectocycloceras Ulrich et al., 1944, differs in having straight sutures and a thin marginal sipuncle. Walcottoceras, which is otherwise similar, differs in having a marginal siphuncle along the concave side of the conch. EORUDOLFOCERAS ANTIQUUM (Flower, 1964) Figures 5.2, 5.3, 7.6, 7.7, 7.9, 7.10 Rudolfoceras antiquum FLOWER, 1964, p. 129, pl. 7, figs. 17, 18.

Diagnosis.⎯Eorudolfoceras species with elongate, weakly compressed conchs with strongly oblique undulations; undulations slope approximately 30⬚ toward the aperture on the convex side of conch. Undulation is not bilaterally symmetrical. Sutures slightly oblique (ca. 5⬚) to undulations and slope toward aperture at concave side of conch. Siphuncle marginal, narrow, on convex side of conch, has concave segments. Body chamber has length/ cross section ratio of more than 1.5 (diagnosis after Flower, 1964). Description.⎯Conch slightly cyrtoconic in juvenile growth stages, nearly straight in more mature growth stages. Conchs elongate and with low apical angle—adolescent conch (NYSM 17353) changes in diameter from 4 mm to 11 mm over a distance of 32 mm while nearly adult conch (NYSM 17357) expands only from 18 mm to 19 mm over a length of 30 mm. NYSM 17357 is largest specimen in NYSM collection, with 19 mm cross section diameter and 30 mm body chamber length. Cross section slightly elliptical, short axis/long axis ratio of 0.96 in specimen NYSM 17362 where cross section diameter is 8.5 mm, but more compressed in later growth stages. Short axis/long axis ratio of 0.86 in specimen NYSM 17346 where cross section diameter is 12.8 mm. Shell surface undulatory, broadly rounded oblique ribs and valleys form conspicuous lobes on concave side of shell. Undulations irregularly spaced; with 2–5 mm distance between ribs and valleys in specimen NYSM 17360 where cross section diameter is 17 mm. Spacing of undulations generally wider relative to cross section diameter in juvenile specimens—with approximately three occurring along a length comparable to the cross section diameter (Fig. 7.10), while five undulations occur along a length comparable to cross section diameter in adult growth stages (Fig. 7.9). Undulations less oblique in juvenile growth stages. Undulation is not bilaterally symmetrical as saddles shift alternatively toward right or left flank (Fig. 7.9). Sutures slightly oblique, slope toward aperture on convex side of conch and form shallow lateral lobe. Ten to eleven chambers occur along length comparable to cross section diameter. Siphuncle marginal on convex side of conch, diameter ca. 0.3 times cross section diameter in specimens NYSM 17346 and NYSM 17362. Connecting ring thick, and with concave segments (Fig. 5.2). Material examined.⎯Fifteen specimens in the NYSM collection from the Wolf Hollow and Canyon Road members, upper Tribes Hill Formation; NYSM localities 5927 and 5896 from Washington County, eastern New York. The NYSM Paleontology Collection also has another 120 specimens of Eorudolfoceras; however, these conchs are not identifiable to species as the sutures are not preserved. These specimens come from eastern New York localities in the Lake Champlain lowlands (NYSM localities 5927, 5896, and TRQ-32) and the Mohawk Valley (NYSM localities 6309, 6311).

Occurrence.⎯The species is known only from the upper Tribes Hill Formation in the Lake Champlain lowlands and possibly from the Mohawk River valley.

Discussion.⎯Eorudolfoceras antiquum differs from E. praenuntium in having strongly oblique, asymmetrical undulations. EORUDOLFOCERAS

PRAENUNTIUM

Flower, 1964

Figure 7.8 Rudolfoceras praenuntium FLOWER, 1964, p. 129, pl. 7, figs. 15, 16. Walcottoceras praenuntium (FLOWER). DZIK, 1984, p. 20, pl. 7, text-fig. 2.25.

Diagnosis.⎯Eorudolfoceras species with weakly obliquely undulated conchs and strongly oblique sutures; sutures slope ca. 20⬚ toward aperture at convex side of conch and have shallow lateral lobes. Cross section weakly compressed. Siphuncle marginal, on convex side of conch, measures ca. 0.3 of cross section diameter, and has concave segments. Body chamber has length/cross section diameter ratio of more than 1.5. Conch undulations slope 20⬚ toward concave side of shell (diagnosis after Flower, 1964). Description.⎯Cyrtoconic, elongate conch nearly straight; apical 6.5⬚ in specimen NYSM 17345 (35 mm long conch expands from 9 mm to 13 mm). Cross section compressed, slightly angular along convex side of shell. Undulations with sharp saddles and smooth valleys; approximately three undulations occur in a distance comparable to cross section diameter along the entire conch. Undulations oblique, slope in opposite direction to sutures (i.e., toward aperture on concave side of conch), diverge 20⬚ from transverse direction. Three undulations occur along distance comparable to cross section diameter. Septa oblique, slope 20⬚ to convex side. Approximately eight septa occur along length comparable to cross section diameter. Sutures form shallow lateral saddles. Material examined.⎯One specimen, NYSM 17345, Canyon Road Member, upper Tribes Hill Formation; NYSM loc. 5896, Washington County, Lake Champlain lowland, New York. As detailed above under Eorudolfoceras antiquum, an additional 120 specimens of Eorudolfoceras in the NYSM collection do not have preserved sutures, and might include conchs referable to E. praenuntium. Occurrence.⎯The species is known from the upper Tribes Hill Formation, Lake Champlain lowlands, and, possibly, from the Mohawk River valley, eastern New York.

Discussion.⎯Eorudolfoceras praenuntium differs from E. antiquum in having strongly oblique sutures. The undulations on its conch are less pronounced than in E. antiquum and less oblique as they slope only 20⬚ toward the concave side of the shell. Genus EREMOCERAS Hyatt, 1884 Type species.⎯Cyrtoceras syphax Billings, 1865, from carbonate debris flow boulders in the Le´vis Formation, Tremadocian, Point Le´vis, Que´bec, Canada. Emended diagnosis.⎯Ellesmeroceratid genus with slightly cyrtoconic, smooth or faintly transversally striated conch that has a slightly compressed cross section and shallow lateral sutural lobe. Sutures with small subangular saddle on prosiphuncular side of conch. Siphuncle marginal or close to margin on concave side of shell. Siphuncular segments concave, consist of thick connecting ring. Septal necks are short and orthochoanitic or hemichoanitic and slightly loxochoanitic. Endosiphuncular diaphragms known. Comparison.⎯Ellesmeroceras conchs differ in being orthoconic in more mature growth stages, cyrtoconic in juvenile growth stages, and have a smaller apical angle. Annoceras differs in having a conch with irregular and shallow undulations, and a more compressed cross section with angular margins at prosiphuncular side. Clarkoceras differs in having a more cyrtoconic conch with a larger apical angle. Occurrence.⎯Lower Ordovician; North America, North China, South Korea.

Discussion.⎯The emended diagnosis largely follows Hyatt (1884, p. 282), Ulrich et al. (1943, p. 126), and Furnish and Glenister (1964, p. K140), who emphasized the cyrtoconic growth axis of Eremoceras, by comparison with the otherwise similar Ellesmeroceras. As early growth stages of the Ellesmeroceras conch

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO are also cyrtoconic, this has caused much confusion in distinguishing Eremoceras and Ellesmeroceras. Foerste (1921) and Flower (1964) faced this problem by providing a differential diagnosis of the ventral and dorsal conch curvature. However, a conch can develop a straight or bent curvature along the prosiphonal side regardless of the general trend of the growth axis. Thus, their distinction between Eremoceras and Ellesmeroceras is very vague as it relied on curvature of the conch outline. Foerste (1921, p. 263) noted in the description of Eremoceras syphax (Billings, 1895) that ‘‘The ventral side is either straight or too faintly concave to be measured,’’ while Ellesmeroceras scheii has a ‘‘Conch straight along the ventral side and presumably straight also along the dorsal side.’’ Flower (1964, p. 45) concluded ‘‘Less satisfactory is the generic boundary between Ellesmeroceras and Eremoceras. Eremoceras is now treated as confined to shells showing more marked modification of the living chamber and more obviously endogastric in the generally slightly greater convexity of the dorsal outline.’’ However, Flower’s (1964, p. 49) diagnosis of Eremoceras was completely inconsistent with this proposal: ‘‘Eremoceras is here restricted to nearly straight compressed shells differing from Ellesmeroceras in showing more definite traces of the primitive endogastric condition.’’ In order to avoid such ambiguous recommendations, we suggest a strict character designation—with Eremoceras characterized by a conch that is cyrtoconic through its ontogeny, while Ellesmeroceras has cyrtoconic conchs only in juvenile growth stages. This distinction is in good agreement with the original diagnoses of Eremoceras and Ellesmeroceras. Thus, Hyatt (1884, p. 282) originally emphasized the bent conch of the genus in his short diagnosis, ‘‘Eremoceras includes arcuate Silurian species with open apertures.’’ Similarly, Foerste (1921, p. 266) emphasized the essentially straight conch of Ellesmeroceras several times in his description of E. scheii. Ulrich et al. (1943) characterized Eremoceras as breviconic. We avoid this term in our diagnosis because the conch of Eremoceras syphax lies at the vague border of what might distinguish breviconic from longiconic. These latter terms are only of value in a differential diagnosis when comparing different species. EREMOCERAS

TERES

Ulrich, Foerste, and Miller, 1943 Figure 6.1

Eremoceras teres ULRICH, FOERSTE, AND MILLER., 1943, p. 131, pl. 60, figs. 5–12; UNKLESBAY, 1954, p. 648, pl. 71, figs. 14–17; FLOWER, 1964, p. 46, 50.

Diagnosis.⎯Eremoceras species with comparably low apical angle (ca. 8⬚–9⬚) and only slightly bent growth axis. Cross section slightly compressed. Sutures form broad rounded lateral lobes and shallow subangular saddles on prosiphuncular side with height less than the distance between two chambers. Siphuncle marginal, diameter approximately 0.3–0.4 times conch cross section (diagnosis after Ulrich et al., 1943). Description.⎯The single specimen recovered in this study is 42 mm long, with maximum cross section diameter of 20 mm and 13.5 mm diameter at adapical end. Growth axis very slightly curved; conch cross section compressed, elliptical, with small axis/large axis ratio of 0.88. Outer shell smooth at cross section diameter of 16 mm, with thickness of 0.56 mm (⫽0.035 of cross section diameter). Approximately 17 chambers occur in distance comparable to cross section diameter. Sutures have rounded lateral lobes and shallow saddles on prosiphuncular side of conch. Internal characters not exposed. Material examined.⎯Two specimens NYSM 17311 and NYSM 17326 from the Wolf Hollow Member of the upper Tribes Hill Formation; hilltop outcrop north of Rte. 22 east of Comstock (NYSM Loc. 5927), Washington County, New York. Occurrence.⎯Tremadocian, Lower Ordovician; widespread in North America.

Discussion.⎯The species differs from all other Eremoceras species in having a low apical angle, a comparatively rounded cross section, and a wide siphuncle.

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AKNOWLEDGMENTS

J. W. M. Thompson and D. Levine, National Museum of Natural History, Smithsonian Institution, Washington, DC, and J. A. Spielmann, New Mexico Museum of Natural History and Science, Albuquerque, counted the Tribes Hill specimens in their collections. We are grateful to David Evans, Peterborough, UK, and Matilde Beresi, Mendoza, for their careful reviews and helpful comments. B.K. is grateful to D. Korn, Museum fu¨r Naturkunde, Berlin, for his support. The NYSM funded B.K. for this study. REFERENCES

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NYSM locality 5896.⎯Canyon Road Member, upper Tribes Hill Formation, lower Lower Ordovician (upper Skullrockian); pasture overgrown with heavy second growth, ca. 250 m north of Rte. 149 which runs east from Smith Basin to Hartford and ca. 1.6 east of Smith Basin village, Washington County, New York. R. H. Flower collected between 1945 and 1947 at this locality, and the light colored, massive limestone lithology represents his ‘‘Smith Basin Limestone’’ (Flower, 1968). Approximately 268 nautiloid specimens are in the NYSM collection. In the 1940s, the locality was a very small quarry, but is now overgrown. NYSM locality 5898.⎯Wolf Hollow Member, upper Tribes Hill Formation, lower Lower Ordovician (upper Skullrockian); cuesta-top exposure approximately 200 m west of turn to east of abandoned dirt road that runs north of Rte. 149 (i.e., Smiths Basin–Hartford road) and runs along Kingsbury–Hartford town line, Washington County, New York. R. H. Flower collected in 1947 at this locality and left 32 nautiloid specimens in a medium gray, sparse fossil wackestone in the NYSM collection. Flower’s field notes indicate he believed this was an ‘‘Upper Cambrian’’ nautiloid assemblage which he referred to the ‘‘Wood Creek Limestone’’ (a stratigraphic designation which was never formalized or published). Subsequently, Fisher (1984) mapped this small limestone outcrop area as Upper Cambrian ‘‘Whitehall Formation’’ (now Little Falls Formation; see Landing et al., 2003). The outcrop is heavily overgrown today, and we found only very small areas of bedrock exposure in May 2005. Acid disaggregation of cuttings from Flower’s specimens (i.e., NYSM locality 5898) and samples collected at the locality yielded Rossodus manitouensis Zone (upper Skullrockian) conodonts (E. Landing, personal data, 2005). These data and the dark color of the massive limestone indicate that Flower’s ‘‘Wood Creek Limestone’’ is a fault-bounded, down-dropped block of Wolf Hollow Member limestone. Dakeoceras champlainense n. sp. from this locality is also known elsewhere from the upper Tribes Hill Formation—from the Wolf Hollow Member (NYSM locality 5927) and Canyon Road Member (NYSM locality 5896). NYSM locality 5927.⎯Wolf Hollow Member, Tribes Hill Formation, west face and top of 132 m (440 foot) hill north of Rte. 22 (Comstock–Granville road), ca. 2,000 m east of Champlain Canal and northwest of the electric power transformer station on the north side of Rte. 22, Washington County, New York. R. H. Flower collected between 1945 and 1947 at this locality, and 114 specimens are in the NYSM collection. The outcrop is heavily overgrown today. NYSM locality 6306.⎯Lower Canyon Road Member (⫽‘‘Fonda Member’’ of Fisher, 1954), Tribes Hill Formation; abandoned quarry north of Mohawk River, ca. 60 m north of Route 67, 2 mi (approximately 3.3 km) north-northeast of village Tribes Hill village, Montgomery County, New York (see Landing et al., 1996, fig. 2, Route 67 locality). Specimens collected by D. W. Fisher before 1954. NYSM locality 6309.⎯Lower Canyon Road Member (⫽‘‘Fonda Member’’ of Fisher, 1954), upper Tribes Hill Formation; exposures 2 mi (ca. 3.3 km) east of village Fort Hunter abandoned quarry on hill to the south of the dirt road; along West Shore Railroad; and abandoned quarry north to the tracks extending down to the Erie Canal, Montgomery County, New York. This is the section Cleland (1900, 1903) collected from; D. W. Fisher collected the specimens before 1954. NYSM locality 6311.⎯Lower Canyon Road Member (⫽‘‘Fonda Member’’ of Fisher, 1954), upper Tribes Hill Formation; abandoned quarries along the north side of the abandoned N.Y. Central Railroad, just east of the Tribes Hill central depot, Montgomery County, New York. D. W. Fisher collected the specimens before 1954. NYSM locality 6318.⎯Sprakers Member (⫽‘‘Fort Johnson Member’’ of Fisher, 1954), lower Tribes Hill Formation, Early Ordovician; abandoned quarry on east side of Canajoharie village, immediately south of U.S. Rte. 5S, and old West Shore Railroad, Montgomery County, New York (see Landing et al., 1996, fig. 3, Canajoharie locality). NYSM locality 6326.⎯Wolf Hollow Member (⫽‘‘Chuctanunda Creek Member’’ of unpublished notes of D. W. Fisher that accompanies specimens), upper Tribes Hill Formation; road cut at bend of the country highway leading north and then sharply northeast, approximately 1,000 m from intersection in Nelliston, Montgomery County, New York. Specimens collected by D. W. Fisher before 1954. (The ‘‘Chuctanunda Creek’’ Member or Formation of Fisher, 1954, simply referred to the uppermost Tribes Hill Formation, but as

¨ GER AND LANDING—EARLY CEPHALOPODS OF TRIBES HILL FORMATION KRO at locality 6326 also included hydrothermally dolomitized areas of the Tribes Hill near block faults in the Mohawk River valley, Landing et al., 1996.) NYSM locality 6328.⎯Wolf Hollow Member, Tribes Hill Formation; field exposures and road cuts extending from U.S. Rte. 5S southward for 500 m to the first high ridge, one mi (approximately 1,600 m) southwest of Little Falls, Herkimer County, New York. Collected by D. W. Fisher before 1954. NYSM locality 9527.⎯Lower Canyon Road Member; sample CCr-10.6

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from section in Canajoharie Creek in Canajoharie village, Montgomery County (see Landing et al., 1996, fig. 3, Canajoharie Creek section). E. Landing collected two specimens of Ectenolites in 1990 from this horizon. NYSM locality TRQ-32.⎯Sample TRQ-32 from uppermost Wolf Hollow Member, upper Tribes Hill Formation; top surface exposed in abandoned Tristates Quarry just north of the intersection of U.S. Rte. 4 and Buckley Road and 700 m east of Whitehall village, Washington County, New York (see Landing et al., 2003, fig. 4, Tristates Quarry section).