500
Journal of Paleontology 92(3):488–505
Materials.—UMMP 74678.3 (Bobcaygeon-Verulam contact zone, LaFarge Quarry).
Remarks.—Cleiocrinus holdfasts are morphologically dis- tinctive and can be assigned to the genus with confidence. The holdfast structure is a high inverted cone comprised of small, intergrown plates that encrust the underlying surface. The center of the cone is deeply depressed, and the distal stem rests within the depression. It is probable that the specimen examined here belongs to C. regius, but a specific assignment cannot be made with certainty.
Family Rhodocrinitidae Roemer, 1855
Remarks.—Recent phylogenetic analyses of Ordovician camerates (Cole, 2017) reinforce the long-held suspicion that Rhodocrinitidae is a polyphyletic group. The family is in need of substantial systematic revision, but such an undertaking is beyond the scope of this manuscript because it requires a com- prehensive phylogenetic analysis of Diplobathrida. Despite this issue, the name Rhodocrinitidae is maintained herein because there is not yet an alternative classification that reflects the evolutionary relationships of diplobathrids at the family level. It is possible that some of the taxa assigned herein to Rhodocri- nitidae will require reassignment to a different family once a revised, phylogenetically informed classification is completed.
Genus Archaeocrinus Wachsmuth and Springer, 1881 Type species.—Archaeocrinus lacunosus (Billings, 1857).
Diagnosis.—Rhodocrinitid with a medium to high conical or globose calyx; infrabasals small, restricted to basal concavity; basals large; regular interrays in contact with tegmen, proximal plating 1-2; CD interray wider, proximal plating 1-3, forming an anal series; arms 10, uniserial or biserial, branching isotomously.
Occurrence.—Middle–Upper Ordovician (Darriwilian–Katian); United States (Oklahoma, New York, Kentucky, Virginia, Tennessee) and Canada (Ontario, Quebec).
Remarks.—Springer (1911) reported both A. microbasalis and A. lacunosus from the region of Kirkfield. However, all speci- mens examined from the Brechin region differ significantly from previously described species. This suggests previous spe- cific identifications of Archaeocrinus from Kirkfield may have been in error.
Archaeocrinus sundayae new species Figures 5.4, 7.1–7.8
Holotype.—UMMP 74682, holotype; UMMP 74683, paratype; UMMP 74684, paratype.
Diagnosis.—Archaeocrinus with lobate globose to bowl- shaped calyx; weakly defined median ray ridges; lack of plate ornamentation; fixed pinnules numerous, preventing contact of interrays with tegmen; regular interrays with few (<10) plates; posterior interray with additional plates and weak anitaxial ridge; fixed brachials bifurcating once within the calyx, giving rise to 10 arm openings; arms biserial, pinnulate, poorly isotomously branched.
Occurrence.—Material described and figured here is from the Upper Ordovician (lower Katian) Bobcaygeon-Verulam contact zone, Carden Quarry. Two additional specimens (CMCIP 54029) examined are referred to A. sundayae n. sp., which are from the Upper Ordovician (Katian) Curdsville Formation, Garrard Co., Kentucky, on highway KY 34, just east of the bridge crossing Herrington Lake.
Description.—Calyx bowl-shaped to globose, slightly wider than high, lobate where arms become free; plates lacking orna- mentation; plate sutures clearly visible, flush with plate surface; base of calyx concave without any surrounding ornamentation; median ray ridges faintly convex. Infrabasals not observed, missing (UMMP 74682) or
completely hidden by column (UMMP 74683). Basal circlet truncate proximally, forming rim of basal concavity; basal plates five, hexagonal, almost entirely visible in side view, slightly wider than high. Radial circlet interrupted in all rays by contact of basals and
primanal and with first interradial plates; radial plates five, hexagonal in C and D rays, pentagonal in all other rays, slightly wider than high, equal in size to basal plates. Regular interrays not in contact with tegmen, not
depressed, interrupting the radial circlet in all rays. First interradial plate heptagonal, as wide as high, slightly larger than radials and basals. Second range with two plates; proximal plating 1-2-3-2-2 or 1-2-2-2 followed by higher rows of very small plates and fixed pinnules. Posterior interray about as wide as regular interrays, not
in contact with tegmen; primanal heptagonal, wider than high, smaller than first interray plates; proximal plating P-3-3-3-5-3-4, followed by higher rows of fixed pinnules; faint anitaxial ridge along medial column of plates. First primibrachial fixed, hexagonal, wider than high;
second primibrachial axillary, pentagonal. Secundibrachials fully fixed into calyx to about fifth secundibrachial, proximal brachials above fifth secundibrachial becoming biserial and forming lobate arm bases attached to the calyx by fixed pinnules; second, fourth and fifth secundibrachials giving rise to fixed pinnules on alternating sides of each half ray, higher secundibrachials all giving rise to fixed pinnules grading into free pinnules in higher brachials. Fixed intrabrachials between secundibrachials of each half ray comprised of a single plate or followed by up to two rows of one or two plates each; higher
Figure 7. Archaeocrinus sundayae n. sp. from the Bobcaygeon-Verulam contact zone, Carden Quarry, southern Ontario. (1, 4, 7, 8) UMMP 74682, holotype; (1) CD interray view; (4) E ray view; (7) adoral view of calyx base, CD interray oriented down (8) aboral view of tegmen and anal tube, CD interray oriented down; (2, 3, 5) UMMP 74683, paratype; (2) close-up of crown; (3) lateral view of complete specimen; (5) close-up of holdfast; (8) juvenile specimen UMMP 74684, paratype, lateral view of complete crown and proximal stem. All scale bars 5mm.
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