INVERTEBRATES. 243 



and really looking very much like a diminutive arm rising from the middle of 

 the anal area.- This arm-like range of small pieces seems never to consist of 

 more than from four to six or seven pieces, which are so small and narrow as to 

 leave a wide, free, open space between them and the posterior rays on each side, 

 as seen in our figure of Onychocrinus monroensis, plate 17, figure 7. How they 

 connect with the vault we have never been able to make out, as they are always 

 entirely disconnected from all other parts, excepting the subradial upon which 

 they rest. We suspect, however, that they merely formed the outside of a 

 small lateral proboscis, the inner side of which was composed of a soft, dermal 

 integument, connecting with the vault. 



This peculiarity of the anal side has been entirely overlooked, or misunder- 

 stood in the species of this type 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 Forbesiocrinus monroensis and 

 F. Nbrwoodi, which belong to this group (though not extreme examples of it), 

 is only occupied by a slender little finger-like appendage, resting upon the upper 

 side of the odd subradial; but as stated in our description of the former species, 

 we supposed the anal plates had been broken out, and that this little round, 

 finger-like appendage, occupying their place, was one of the smaller divisions 

 of the arms that had been accidentally placed in that position, in the only speci- 

 men of each of these species then known. Lyon and Casseday had, however, 

 correctly described these as the anal pieces of Onychocrinus. 



We have seen this character well defined in the following species, viz : For- 

 besiocrinus aster ise for mis, F. Whitfieldi and F. Meeki, of Hall ; and in our F. 

 monroensis, F. Norwoodi and 0. diversus, as well as in Lyon and Casseday's 

 typical species. In the type of the species F. Meelci, now before us, the anal 

 area, as may be seen by the figure in the Iowa Report, is entirely open, and 

 even without the little finger-like appendage, which was broken out. In five 

 other individuals, however, of this species we have seen, this character is un- 

 mistakably visible, and we have never seen a specimen of either this or any of 

 the other species mentioned above, with the anal side filled with plates as in 

 Forbesiocrinus. 



From all the facts now known, we therefore incline to the opinion that these 

 forms should be separated from Forbesiocrinus, under the name Onychocrinus. 

 It is worthy of note, however, that this group seems to be even farther divisi- 

 ble into two rather distinct sections, upon characters the exact value of which 

 we cannot satisfactorily determine without knowing more about the vault and 

 upper side of these species. For instance, 0. asterixformis= (Forbesiocrinus 

 asterise/ormis, Hall), and our 0. diversus, which are the extreme forms already 

 referred to, differ from the other species mentioned, in having the rays more 

 spreading, and free in as far as to the second or first primary radials, instead 



