TWO NEW RARE ORDOVICIAN ECHINODERMS FROM CENTRAL TENNESSEE

Ordovician echinoderms from central Tennessee are relatively poorly known compared to adjacent strata of the Cincinnati Arch. New species of Ordovician echinoderms from this region are seldom reported, with the exception of the Lebanon Limestone fauna, even though these rocks are well exposed throughout the central basin. Here we report on a new species of cyclocystoid and a new genus of solute from the Upper Ordovician carbonates of the Nashville Dome. The cyclocystoid Polytryphocycloides n. sp. is described from the Catheys Formation (Katian, Shermanian) and is known from a single specimen on a dark purplish-gray fine-grained grainstone with abundant brachiopods and bryozoans. The articulated marginal ring, partially covered by a Hebertella brachiopod, displays roughly 42-43 marginal ossicles, of which only the surface opposite the cupules is exposed. This dorsal surface displays a rugaceous ornamentation unique to the genus. Based on marginal breadth and partial weathering of the marginals, each exposed ossicle bears two cupules. The discoidal test exhibits a maximum width of 33 mm with the disc comprising 82% of the total width. The marginal ossicles, longer than broad, possess an average maximum breadth of 2.3 mm and an average length of 2.9 mm. The peripheral skirt is recumbent on the cupule bearing surface and comprises at least seven imbricate rows of plates. Several features of the cyclocystoid skeleton suggest flexibility in life, and we here present interpretations of these data with regards to the autecology of this enigmatic group.

A new genus of belemnocystitid solute from the Lebanon Limestone (Sandbian, Black Riveran) is represented by a single specimen. The complete ventral surface of the theca is preserved, but information on the dorsal surface or feeding structures is unknown. The proximal stele is present but disarticulated and poorly preserved. This genus is unique in having marginal plates wider than ventral somatic plates. The A4 somatic plate is absent in this genus, replaced by an enlarged M10 marginal. Each plate displays a pustulous ornamentation. The theca is ovoid and has a maximum length of 24 mm and a maximum width of 19 mm. This specimen is situated on a gray, bioturbated, silty wackestone with associated starfish and crinoids.