Abstract

Two zones in the Cave Hill member contain the aberrant crinoid Pterotocrinus Lyon and Casseday, with P. edestus n. sp., P. tridecibrachiatus n. sp., and P. wahlessi n. sp. in the lower and P. pegasus n. sp. in the upper. More than 2,000 wing plate and two complete calyces show that in contrast to the usual 20 biserial arms of early Chester species, the Kinkaid species have 30 biserial arms and a modified brachial plate arrangement, necessitating emendation of the genus and elucidating its phylogeny within the Chester.

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