CYSTOIDS OF THE COEYMANS FORMATION, HELDERBERG GROUP, NEW YORK STATE: A NEW SPECIES OF LEPOCRINITES AND LEPOCRINITES GEBHARDI REVISITED

The rhombiferan cystoid Lepocrinites gebhardi is a characteristic member of paleocommunities in parts of the Coeymans Formation. The Ravena and Deansboro members of the Coeymans Fm. contain numerous specimens of large disarticulated adult L. gebhardi holdfasts. Thin sections of the tuberous holdfast present a more complex morphology than previously described, with a perforated central lumen bearing regularly spaced dendritic canals connecting the central axis to the exterior, possibly for attachment structures similar to a byssus. The central lumen of gebhardi, which is trigonal in cross section at the base, broadens vertically (by addition of facets) to a nearly circular cross section at the base of the stem. Pore rhombs in complete specimens and disarticulated calyx plates display slight variation, with one raised and reinforced crescentic demi-rhomb.

Numerous specimens of Lepocrinites n. sp. were collected at the type section of the Dayville Member of the Coeymans Fm. Hundreds of complete and slightly disarticulated specimens occur smothered within a single ostracod tempestite. Disarticulated specimens occur sporadically, but are locally abundant, in the Olney Member and Elmwood "C" sub-member of the Manlius Fm. Calyces of this form bear larger, much more robust and angular pore rhombs, that lack the crescentic demi-rhomb characteristic of L. gebhardi. Holdfasts of this new species are similar in dimension to gebhardi, but are more cone-shaped without perforations connecting the central lumen to the exterior.

Recent work by Ebert, et. al. (2001) demonstrates that the Dayville Member (and the Manlius Fm.) is entirely older than the Ravena and Deansboro members of the Coeymans Fm. throughout the escarpment. Specimens from the Olney Member consist largely of juveniles, whereas primarily adults are found within the laterally equivalent (deeper water) Dayville. L. gebhardi and L. n. sp. have yet to be found together. Lepocrinites adapted to the shifting, higher-energy environments of the Coeymans Fm. by developing a more robust holdfast (with byssus?) and modified pore rhombs. The new species represents the evolutionary progenitor of L. gebhardi, and demonstrates a more complex history for this unique genus.