1888.] NATURAL SCIENCES OF PHILADELPHIA. 347 



■of its posterior side bears a striking resemblance to the form under 

 consideration. From all that we can see on our three specimens, and 

 .some examples of Onychocrimis exsculptm, in which a similar set of 

 pLites and parts of the perisome are preserved, we do not believe that 

 there was a second appendage in the disk as in Thaumatocrinus, but 

 think that the row of large plates supported the anus. The shape 

 of the visible portions of the disk varies in the three specimens, and 

 it is evident that the whole perisome was pliant and could be expand- 

 ed or contracted. 



A similar integument has been found betw^een the rays in Taxocrinus 

 rohustus W. and Sp. from the same locality, a new Taxocrinus from 

 the St. Louis limestone, and in Onychocrinus asteriaeformis from the 

 Burlington limestone. In a specimen of Onychocrinus diversus 

 lying on the ventral side, and from which we removed the basal and 

 some of the radial plates, giving an inner view from below, we can 

 see in two rays the alternating subambulacral plates converging near 

 the center, but not the orals nor any part of the perisome. In one 

 of Onychocrinus exsculptus we find remnants of the perisome and 

 traces of the oral plates, however not in position. The last two 

 specimens are those mentioned by us in Revision Pt. I, p. 32, on 

 one of which we based our statement (Rev. I, p. 54), under Onycho- 

 crinus, that "in the median portion of the vault there are six rather 

 thin but large apical dome ])lates", '^vhich we were afterwards in- 

 clined to modif}^ as we could not make out satisfactorily the ar- 

 rangement of the plates (Rev III. pp 20, and 67). In several speci- 

 mens of the last named species we have seen the anal appendage, 

 with the integument extending either way to the rays, and the 

 same thing was long ago observed by Meek and Worthen (Geol. 

 Rei). Illinois., Vol. Ill, p. 494.). 



It is thus evident that the ventral covering of Taxocrinus consist- 

 ed of perisomic plates with external mouth and food grooves, and 

 five oral plates, surrounding the mouth and separated by the ambu- 

 lacra. We have now very little doubt that the structure thus dis- 

 covered is substantially that of the Ichthyocrinidae generally, and 

 that the ventral side of the calyx in this family is morphologically 

 in the condition of Thaumatocrinus, and similar to that o^Hyocrinus 

 and Rhizocrinus. 



Although we have heretofore entertained a different opinion, we 

 yield most cheerfully to the proofs, and we are heartily glad to be 

 the means of bringing to light one substantial fact to take the place 



