NATURAL SCIENCES OF PHILADELPHIA. 255 



Locality and position.:- Burlington, Iowa. Lower beds Burlington group of 

 the Subcarboniferous series. Mr. Wachsinuth's collection. 



Genus ONYCHOCRINUS, Lyon and Casseday, 1859. 

 Although for some time past inclined, like others, to regard the type for 

 which the name Onychocrinus was proposed, as probably in no respect distin- 

 guishable from Forbesiocrinus, recent comparisons of some fine examples of 

 these forms lead us to think that they may be even generically distinct. At 

 any rate, they are certainly distinguishable upon more constant characters 

 than those separating Forbesiocrinus from Taxocrinus, which groups we have 

 elsewhere shown* blend together to such an extent that we do not think they 

 can be separated more than subgenerically, upon any characters yet pointed 

 out. 



At present we are inclined to regard Onychocrinus as being generically dis- 

 tinct from Forbesiocrinus and Taxocrinus, but it may possibly form a second 

 subgenus under Taxocrinus. I* the nature of the column, the number and 

 arrangement of the basal, subradial and primary radial pieces, Onychocrinus 

 agrees exactly with Forbesiocrinus : while in other points of structure these 

 types differ to an extent that could scarcely fail to attract the attention of the 

 most careless observer, on comparing good specimens of each. In the first 

 place, Onychocrinus differs from Forbesiocrinus in having the rays from their 

 origin more divergent, or even income instances extending out horizontally 

 on the same plane with the base ; while in these extreme cases the long rays, 

 which are free in to the second radial pieces, and bear the small arms in 

 clusters at their extremities, have their under sides rounded, and their lateral 

 margins curved up on each side to meet apparently a series of pieces covering 

 them over above. According to Lyon and Casseday these forms also have 

 the vault covered over with solid calcareous pieces a character not known to 

 occur in Forbesiocrinus. Another difference is always observable in the anal 

 side of these types, which in Onychocrinus, instead of being occupied by as 

 many pieces a| the interradial spaces, or a larger number, as in Forbesio- 

 crinus, is often so deeply excavated as to destroy the symmetry of the body, 

 and only occupied by a single row of very small pieces, mounted one upon 

 another," and resting in a sinus in the upper side of the largest subradial, so 

 as to look much like a little dwarfed simple arm. On each side of this little 

 arm-like range of anal pieces, there is a free open space between it and the 

 adjacent rays, whatever may be the number of pieces filling the interradial 

 spaces between the other rays. How this range of little anal pieces (of which 

 there never seems to be more than six or eight) connects with the vault, we 

 have been unable to determine, as they are always, so far as we have had an 

 opportunity to see, entirely disconnected from all parts of the body, excepting 

 the single subradial upon which they rest. We suspect, however, that they 

 may have formed tne outside of a small lateral proboscis, the inner side of 

 which was merely covered by a soft dermal integument. 



This peculiar character of the anal side, in Onychocrinus, seems to have 

 been entirely overlooked or misunderstood in the species of this group referred 

 to Forbesiocrinus the impression being that the anal plates had been, by 

 some accident, removed from their place. It is true, we had observed that 

 the anal area in our F. monroensis and F. Noriooodi is only occupied .by a 

 slender little finger-like appendage, resting upon the upper side of the large odd 

 subradial, but, as stated in our remarks in relation to the former species, we 

 supposed the anal plates had been removed, and that the little rounded finger- 

 like appendage occupying their place, was only one of the smaller subdivisions 

 of One of the arms that had been accidentally placed in that position. We 

 have seen this character, however, in the following species, which we have 

 in the Illinois Report referred to Onychocrinus, viz., Forbesiocrinus aster iwfor- 

 mis, F. Wldtjieldi and F. Meeki, Hall ; also in our F. monroensis and F. 

 Norwsodi, as well as in the new species described in this paper. In the typi- 



* Proceed. Acad. Nat. aci. Philad., Aug., 1865, p. 138. 



1868.] 



