494
Journal of Paleontology 92(3):488–505
Occurrence.—Reteocrinus alveolatus was previously known from Upper Ordovician (Katian) occurrences in the Curdsville Member of the Lexington Formation, Kentucky and from the Hull Formation, Ottawa Group, Ontario. The occurrences reported here are from the Bobcaygeon-Verulam contact zone, LaFarge and Carden Quarries, Upper Ordovician (lower Katian).
Description.—Calyx straight-sided cone to height of radials, cylindrical above radials with straight or slightly convex sides, higher than wide, lobate; crown about twice as high as maximum calyx width. Cup plates deeply cleft, smooth, with multiple rounded limbs; fixed brachial plates smooth or orna- mented with faint, irregular, discontinuous ridges; brachials thick, raised from surface of calyx, forming prominent rounded median ray ridges; plate sutures flush with surface of plates. Infrabasal circlet upright, entirely visible in side view;
Lumen small, circular, surrounded by five small canals, unconnected to the lumen, positioned in the stem lobes. Holdfast circular to subcircular, composed of many small, smooth, irregular plates, commonly with a central depression where the stem attaches, cemented to the seafloor, diameter approximately equal to that of the calyx.
Materials.—UMMP 74672 and 74673 (Bobcaygeon-Verulam contact zone,LaFargeQuarry);UMMP 74671, 74674, 74675, and 74677.1 (Bobcaygeon-Verulam contact zone, Carden Quarry).
Remarks.—Although R. alveolatus has been previously descri- bed from abundant material, the tegmen and anal tube was not previously known. The description given here includes details of these structures, which are preserved in UMMP 74675.
infrabasal plates five, wider than high, nearly as large as basals. Interinfrabasal gaps small and deep, not in contact with stem margin, shape variably triangular, subrounded, or diamond-shaped. Basal circlet entirely visible in side view; basal plates x- or
y-shaped, approximately as high as wide, largest plates in calyx; CD basal plate pentaxial (stellate with five rays), usually higher than wide, supporting primanal. Interbasal gaps deeply depressed, diamond-shaped to semi-circular, filled with small, irregularly arranged stellate plates similar to plating of interrays. Radial circlet interrupted in all interrays; radial plates five,
inverted y-shape, higher than wide, smaller than basals. Regular interrays narrow, depressed, in contact with
tegmen, maintaining equal width or constricted only in distal- most portion. Interray plating irregular, consisting of many small polygonal plates; interray plates with coarse stellate ornamentation, presumably not rigidly cemented. Posterior interray wider, in contactwith tegmen; anal series
conspicuous, ray-like, comprised of a single column of 10 or more narrow plates originating from the CD basal and continuing onto the tegmen; primanal rectangular, about three times higher than wide, higher plates in series decreasing slightly in size; anal series flanked by narrow, depressed areas with plating identical to that of regular interrays. Primibrachials two to five, variable within specimens; first
primibrachial quadrangular, slightly wider than high. Secundibra- chials typically three, less commonly two or four, variable within specimens, approximately as high as wide. Fixed intrabrachial plates within rays, plating similar to that of regular interrays. Arm openings probably 20, ungrouped, position at which
arms become free indistinct. Free arms apinnulate, poorly isotomously branched, up to six bifurcations in fixed and free brachials combined; brachials rectilinear uniserial. Anal opening unknown.
Tegmen contiguous with interrays, sac-like, reaching to the
height of the arms, terminating in a rounded tip; tegmen plates small, nodose to coarsely stellate, irregularly arranged, similar to interray plates. Stem pentameric, heteromorphic N333233313332333
where fully differentiated, stem meres thin; proximal stem pentastellate to pentalobate, gradually expanding near the base of the calyx, commonly with sharp ridges running lengthwise along axes of pentastellate stem; medial stem grading into pentagonal shape; distal stem circular to obscurely pentagonal.
Infraclass Eucamerata Cole, 2017
Order Diplobathrida Moore and Laudon, 1943 Superfamily Rhodocrinitoidea Roemer, 1855
Family Anthracocrinidae Strimple and Watkins, 1955 Genus Priscillacrinus new genus
Type species.—Priscillacrinus elegans new species, by monotypy.
Diagnosis.—As for species, by monotypy.
Etymology.—The genus name Priscillacrinus is in honor of Priscilla Wright, mother of D.F. Wright.
Remarks.—Superficially, Priscillacrinus n. gen. appears similar to the rhodocrinitid Diabolocrinus, but is differentiated by its additional bifurcation within the fixed brachials. Priscillacrinus n. gen. is assigned to Anthracocrinidae on the basis of its basal concavity involving infrabasals and partial basals, prominent median ray ridges, fixed brachials bifurcating twice within the calyx, regular interray plating 1–2withthe first interray plate enlarged, 20 free armopenings, and fixed pinnules. Additionally, phylogenetic analysis recovered Priscillacrinus n. gen. within the anthracocrinid clade (Fig. 2). In the recovered tree, Priscillacri- nus n. gen. ismost closely related to Cotylacrinna, a diplobathrid from the Middle Ordovician of Iowa (Brower, 1994). Morpho- logically, Priscillacrinus n. gen. and Cotylacrinna share many features including a low, lobate calyx; thick calyx plates; inter- rays with proximal plating 1-2-3; at least two brachial bifurca- tions with the second branching occurring where arms become
free; fixed intrabrachials between half rays but not quarter rays; fixed pinnules; and flat chisel biserial brachials. Priscillacrinus n. gen. differs from Cotylacrinna in that it possesses heavily ornamented cup plates, no ray lobes built from fixed brachials, multiple fixed pinnules in each ray, two secundibrachials in each quarter ray, and four free arms per ray. In contrast, Cotylacrinna has no plate ornamentation and only weak median ray ridges, distinctive ray lobes built from fixed brachials, fixed pinnules occurring only occasionally in rays, usually four secundibrachials per ray, and four to six free arms per ray.
Priscillacrinus elegans new species Figures 4.1–4.4, 5.1–5.3
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