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Journal of Paleontology 92(3):488–505
rows composed of fixed pinnules preventing contact with tegmen.
Tegmen low, comprised of numerous small plates; tegmen
plates undifferentiated, ornamented with small nodes. Plates covering ambulacral areas convex, showing branching pattern on tegmen; interambulacral areas depressed, interambulacral area opposite the posterior interray with a deep depression. Anal tube cylindrical, positioned subcentrally toward the posterior interray; remnants of small spines projecting from some anal tube plates, presumably originally present on all anal tube plates; total height of anal tube unknown; anal opening presumably from anal tube terminus. Arm openings 10, ungrouped; numerous fixed pinnules
positioned between all arm openings. Free arms poorly isotomously branched, bifurcating twice; first branching typi- cally on the 13th secundibrachial, second branching irregular in height. Brachials wedge biserial throughout free arms. Pinnules on every brachial except axillary arm plates; fixed pinnules stout, robust; distal pinnules longer and thinner. Stem circular, holomeric; heteromorphic in proximal and
medial stem, N3231323, becoming homeomorphic in distal stem. Holdfast composed of ~ 15 terminal rhizoids, clustered on one side of column. Lumen unknown.
Etymology.—The species name sundayae is for Steffanie Sunday, wife of J.M. Koniecki.
Materials.—UMMP 74682, holotype; 74683, paratype (Bobcaygeon-Verulam contact zone, Carden Quarry); and 74684, paratype (Bobcaygeon-Verulam contact zone, Carden Quarry); CMCIP 54029 (two specimens, Curdsville Formation, Garrard Co., Kentucky).
Remarks.—Of the 11 species of Archaeocrinus previously described, several are known from Ontario, including A. marginatus, A. lacunosus, and A. microbasalis. Archaeocrinus sundayae n. sp. is differentiated from other species of Archaeocrinus on the basis of its numerous fixed pinnules, very narrow contact between the interrays and the tegmen, relatively few interray plates (≤10 large plates) in four or five rows, lack of plate ornamentation, faint median ray ridges, and up to two bifurcations in free arms. In contrast, A. lacunosus has no fixed pinnules, interrays in contact with the tegmen, numerous interray plates (>20 large plates), and irre- gular stellate ridges; A. microbasalis has few fixed pinnules, interrays in contact with the tegmen, numerous interray plates in 10 or more rows, striated stellate ornamentation, distinct median ray ridges, and three bifurcations in free arms. Although A. marginatus is poorly known, it differs from A. sundayae n. sp. in that the interrays are comprised of many large plates (>20) in at least seven rows. Archaeocrinus sundayae n. sp. is also very similar to A. snyderi Guensburg, 1984, but the latter differs in that it lacks lobate arm bases, has interrays in contact with the tegmen, has no anitaxis in the posterior interray, lacks tertin- ternodals in the stem, and possesses uniserial arms that bifurcate at least three times. Specimen UMMP 74684 is likely a juvenile form.
Although the specimen is much smaller than other specimens of A. sundayae n. sp. examined, the presumed juvenile specimen
is remarkably similar to adults in terms of interray plating, overall shape, organization of the calyx, and arm construction. The arms of the juvenile specimen display fully developed biserial brachials, which often do not develop until late in ontogeny. This suggests that this species developed adult plating early in ontogeny and then proceeded to grow isometrically through enlargement of plates, rather than continued insertion of plates and/or changes in plate dimensions.
Archaeocrinus maraensis new species Figure 8.1–8.7
Holotype.—UMMP 74685, holotype; UMMP 74686.1, paratype; UMMP 74688, paratype.
Diagnosis.—Archaeocrinus with medium globose calyx; plates with delicate, irregular granular and stellate ornamentation; numerous fixed pinnules; interrays not in contact with tegmen; free arm openings 10; free arms bifurcating isotomously three times; brachials flat chisel biserial; stem strongly heteromorphic.
Occurrence.—Material described and figured here is from the Upper Ordovician (lower Katian) Bobcaygeon-Verulam contact zone, Carden Quarry; and from the lower Verulam Formation, James Dick Quarry.
Description.—Calyx medium bowl-shaped to globose, about as wide as high, arm bases protruding slightly; plates with fine, irregular granular ornamentation and stellate ridges; plate sutures clearly visible, flush with plate surface; base of calyx concave without any surrounding ornamentation; median ray ridges faint, narrow, beginning in center of radial plates. Infrabasals not observed, entirely in basal concavity. Basal
circlet curving slightly at base of calyx but entirely visible in side view, not part of basal concavity; basal plates five, hexagonal, wider than high. Radial circlet interrupted in all rays by contact of basals and
primanal with first interradial plates; radial plates five, pentagonal, 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, similar in size to radials and basals. Second range with two plates; typically 10 or more rows of plates above first interray plate; proximal plating
1-2-3-3-3-3 or 1-2-3-3-2-2 followed by higher rows of three to five small plates each. First primibrachial fixed, hexagonal, wider than high;
second primibrachial axillary, pentagonal or heptagonal. Secundibrachials fully fixed into calyx to about fifth secundi- brachial, proximal brachials above becoming biserial and forming protruding 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. Fixed intrabrachials between secundibrachials of each half ray,
proximal plating usually 1-2-2-2; higher rows comprised of fixed pinnules preventing contact with tegmen.
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