Iocrinus subcrassus

Classification
Phylum: Echinodermata
Class: Crinoidea
Order: Disparida
Family: Iocrinidae
Genus: Iocrinus
Species: Iocrinus subcrassus (Meek & Worthen, 1865)

Stratigraphic Occurrences

I. subcrassus_strat

Geographic Occurrences

		
Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C5 Sequence (Waynesville)
  • C3 Sequence (Mt. Auburn, Corryville)
  • C2 Sequence (Bellevue, Fairview: Fairmount, Mount Hope)
  • C1 Sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)

Identification in Hand Sample

  • Pentagonal stem with a portion of the calyx on top
  • Dominant sculpturing on plates of aboral cup
  • Depressions at triple plate junctions
  • Multi-branched arms with decreased width after successive branching
  • Distinctively plated anal sac is present
Iocrinus_subcrassus_800px

Iocrinus subcrassus from McMillan formation of Brown County, Ohio (OUIP 669)

Published Description

Davis (1998):

  • Crinoid. a: Pentagonal stem with a portion of the calyx on top. b: Pentagonal columnal. c: Calyx and arms (crown)

Fossils of Ohio (1996) :

  • Aboral cup has dominant sculpturing on plates, raised folds on plate centers, and depressions at triple plate junctions; arms have many branches arm width gradually decreases with successive branching; columnals pentalobate (five-lobed)
  • Characterized by a conical aboral cup and dominant ridges and depressions on the cup plates, the arms branch many times and arm width decreases gradually. A distinctively plated anal sac is present. The column is composed of pentalobate (5 lobed) columnals that have a strongly pentalobate pattern on the facets of adjoining columnals.

Meek & Worthen (1965) :

  • This species agrees so nearly with the last in most of its characters as to render a detailed description unnecessary. It will be readily distinguished, however, by its smaller size, as well as its less robust appearance, and the different aspect of its arms. This latter difference consists in the more slender appearance of all the divisions, and particularly in the joints of which they are composed having their upper margins projecting beyond the base of each succeeding piece above, so as to present a kind of upward imbricating appearance and roughness, not seen in the arms of H. crassus. As in the last, its rays bifurcate first on the fifth and sixth pieces, and one of them gives off a branch (?) on the left side of the second radial, above which it bifurcates regularly on the sixth piece. After the first regular division on the last radial piece, some of the arms are seen to divide again on the fourth, others on the fifth, and others on the sixth pieces, after which one division is known to bifurcate on the sixth piece, and still again on the thirteenth. Breadth of body at the summit of the first radial pieces, 0-27 inch ; height of do., 0-13 inch; length of rays from top of first radial pieces to the first bifurcation, 0.21 inch ; entire length of arms from first division to extremities, about 1*50 inches. Breadth of column at its connection with the base, 0-15 inch. Locality and position. —Cincinnati, Ohio. Cincinnati Group of Lower Silurian

Foerste (1924):

  • Fragments of the strongly pentagonal stem are common, but only the basal fragment of one calyx was found. This presents the five basals, strongly depressed along the middle; two the radials, strongly angulate along the middle toward the basal margin; and one of the primibrachs. The strong angulation of the basal part of the calyx is well shown.
  • This species was described originally from some part of the Cincinnatian series of rocks at Cincinnati. The exact horizon is not known. According to Nickles it not only ranges from the Eden through the Maysville and into the Richmond, but it occurs also in the Cynthiana formation beneath the Eden.
  • Locality and Horizon. At the top of the hill on the Sheguiandah road, 3 miles south of LIttle Current (no. 8577). From the limestones in the upper part of the Sheguiandah.