504


Journal of Paleontology 92(3):488–505 Arm openings 10, ungrouped; fixed pinnules positioned


between all arm openings. Free arms isotomously branched, bifurcating three times; first branching typically around the 15th


secundibrachial, second branching occurring shortly above the first; third branching somewhat variable in height. Brachials flat chisel biserial throughout free arms. Pinnules on every free brachial, densely spaced. Stem circular, holomeric; strongly heteromorphic, diameter


of largest nodals more than twice that of smallest intervening internodals; proximal stem N212, medial stem N3231323, distal stem becoming homeomorphic. Lumen pentalobate, ~18% of stem diameter; crenulariumpresent around periphery of columnal facet, but details not well preserved. Holdfast comprised of numerous terminal rhizoids at the end of the column. Tegmen, anal opening, and additional stem features unknown.


Etymology.—The species name maraensis is in reference to the Mara Township where the holotype specimen was recovered.


Materials.—UMMP 74685, holotype (lower Verulam, James Dick Quarry); UMMP 74688, paratype (lower Verulam, James Dick Quarry); UMMP 74686.1, juvenile specimen, paratype (Bobcaygeon-Verulam contact zone, Carden Quarry).


Remarks.—Archaeocrinus maraensis n. sp. is most similar to A. sundayae n. sp., A. microbasalis, and A. snyderi.All four species have fixed pinnules and branched arms, but they differ with regards to the number of fixed pinnules, the condition of the interrays, and features of the free arms. In particular, A.maraensis


n. sp. has free arms that bifurcate at least three times, numerous fixed pinnules, interrays not in contact with the tegmen, flat chisel biserial arms, and fine granulose and stellate ornamentation. Although A.microbasalis has arms that branch three times and flat chisel biserial brachials, it differs fromA.maraensis n. sp. in that it has few fixed pinnules, interrays in contact with the tegmen, and stellate ornamentation. Similarly, A. snyderi has fixed pinnules and arms that bifurcate three times, but it has interrays that contact the tegmen, uniserial arms, and lacks plate ornamentation. Finally, although A. sundayae n. sp. has numerous fixed pinnules and interrays that do not contact the tegmen, it differs from A. mar- aensis n. sp. in that it has arms that bifurcate only twice, wedge chisel biserial arms, and lacks plate ornamentation. UMMP 74686.1 is probably a juvenile specimen of


A. maraensis n. sp.; it shows little morphological differentiation from adult specimens of the species other than its much smaller size compared to other specimens of A. maraensis n. sp.UMMP 74686.1 clearly belongs to A. maraensis n. sp. rather than A. sundayae n. sp. because it has similar stem morphology and irregular stellate ridges and granular ornamentation. Similar to A. sundayae n. sp., however, the juvenile specimen of A. maraensis n. sp. has the same proportions as adult specimens, indicating isometric growth may be common to the genus.


Acknowledgments


We thank B. Hunda (Cincinnati Museum Center) and D. Miller (University of Michigan Museumof Paleontology) for access to museum specimens and assistance with specimen curation. K. Brett is thanked for donating UMMP 74688 for study and


providing comments on an early draft of this manuscript. We thank G. Sevastopulo and B. Deline for providing thoughtful reviews and C. Sumrall for helpful comments. SRC was sup- ported by a J. Thomas Dutro Jr. Student Award from the Paleontological Research Institute, a Presidential Fellowship from The Ohio State University, and a Springer Fellowship from theNMNH(Smithsonian Institution).DFWwas supported by a James R. Welch Scholarship from the Association of Applied Paleontological Sciences and a Peter Buck Fellowship from the NMNH (Smithsonian Institution).


Supplementary material


To view supplementary material for this article, please visit the Dryad Digital Repository: http://doi.org/10.5061/dryad.dd0b1


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