422 SMITHSONIAN INSTITUTION 



Onychocrinus asteriaeformis (Hall) 

 Plate LXIV, figs, i-io 



Forbesiocrinus asteriaeformis Hall, Jour. Boston Soc. Nat. Hist., VII, 1861, p. 320; Descr. New Species 

 Crinoidea, p. 9. — Meek and Worthen, Proc. Acad. Nat. Sci. Philadelphia, IX, 1865, p. 140. — Hall, 

 Bull. 1, New York St. Mus. Nat. Hist., Photographic Plates, 1872, pi. 6, figs. 10, 11. 



Onychocrinus asteriaeformis, Meek and Worthen, Geol. Surv. Illinois, II, 1866, p. 243. — Wachsmuth and 

 Springer, Revision Palaeocrinoidea, I, 1879, p. 54. 



Oligocrinus asteriaeformis, Springer, Amer. Geologist, XXX, 1902, p. 96; Jour. Geology, XIV, 1906, pi. 6, 

 fig. 16. 



The smallest species of the genus. Crown elongate when folded; but fre- 

 quently extended in the form of a five-rayed star, with a broad, shallow calyx 

 in the center. Rays below broad and stout, two and one-half times as long as 

 the rami above; branching after 3 or 4 double series of interlocking IIBr 

 beyond the axillary IBr into 2 small rami; these do not diverge, but continue 

 about parallel and rather close together, giving off ramules on the outside of 

 the dichotom only, tapering gradually to slender extremities and ending in an 

 equal bifurcation. Ramules 3 or 4 to each ramus, long and slender, branching 

 once as a rule; the lowest one sometimes branching twice at short intervals, 

 forming a small cluster. Interbrachials well developed. Sutures slightly 

 arcuate, often appearing straight in lower part of ray. 



IBB low, in form of a thickened columnal. BB of good size, appearing 

 in form of pentagons as high as wide. All brachials relatively short and wide. 

 IBr 3. IIBr united by the inner margins directly or through small iBr to the 

 extent of 4 or 5 pairs in mature specimens, but separating at the axillary in 

 young. First ramule on third IIBr, with intervals of 3 and 4 brachials beyond. 

 First iBr large, with 2 or 3 large ones in second range, diminishing in one or 

 more successive ranges to a rounded crescentic margin about the height of 

 IBr 2 or 3. Anal tube strong, with deep sub-central socket. Column large, 

 tapering slowly from the calyx, and passing into alternating long and short 

 columnal s. 



Dimensions of average of 9 mature specimens: Length of ray below 

 fork, measured from IBB to axil, 25 mm.; of ramus, from fork to axil of 

 terminal bifurcation, 10 mm.; diameter of calyx above IBr, 19 mm.; of base at 

 column facet, 5 mm. 



Hall did not recognize Lyon's genus Onychocrinus, and so placed this extreme form 

 under Forbesiocrinus, which was his favorite dumping ground for Carboniferous Flexibilia. 

 The species was not illustrated when described, but good figures of both type specimens, 

 photographed from drawings by Whitfield, were distributed privately in 1872. I have 

 given new figures of both, with an additional series of five specimens by which all the char- 

 acters are amply illustrated. These are remarkably constant ; in 19 specimens the number 

 of IBr does not vary from 3, except in two rays. 



This is the most extended of all the species in the spreading of the arms, and thus falls 

 readily into the exsculptus group. Tested by the relative lengths of the main ray and of the 



