NEOCRINOIDEA. 445 



five arms, which bifurcate once, and have the power of rolling 

 up. The arms carry a few long pinnules like those of Hyocrinus, 

 and possess small undivided spine-like processes. The skeletal 

 tissue is throughout peculiar in not being dense, but in having a 

 tolerably loose reticulated structure. The characters of Saccocoma 

 are so peculiar, that the genus was placed by Miiller in a separate 

 division of Crinoids, to which he applied the name of Costata. 



APPENDIX. 



Since the preceding pages were written, some important discoveries 

 have been made respecting the nature of the ventral covering in Encrinus 

 and Taxocrinus, the latter genus having a plated disc exactly like that 

 of a Neocrinoid, with open ambulacra and an exposed mouth surrounded 

 by five oral plates. There can be little doubt that the other Ichthyo- 

 crinidcB were essentially in the same condition : while Encrinus proves 

 to be very closely allied to the Carboniferous Poteriocrinidtz, such as 

 Erisocrinns and Stemmatocrinus. 



Under these circumstances, it is no longer possible to regard the 

 Neocrinoidea and PalcBocri?ioidea as well-defined primary groups, though 

 the names may be conveniently retained as expressing a general strati- 

 graphical distinction between the older and the younger Crinoids. Messrs 

 YVachsmuth and Springer have already suggested the outlines of a new 

 classification which, with slight modification by Dr P. H. Carpenter — to 

 whom the author is indebted for the present note — will probably result in 



Order I. Coadunata. 



Crinoids in which the interradials, where present, are incorporated into 

 the calyx, the latter generally also including the higher radials, which are 

 immovably united by suture ; while an anal system is well developed. 

 The mouth and ambulacra are subtegminal, the centre of the vault 

 being occupied by five oral plates, and the arms are usually biserial. 



Sub-order I. Camerata. 



Families — Actinocrinidae, Rhodocrinidae, Reteocrinidae, Glyptocrinidae, 

 Melocrinidae, Platycrinidae, Hexacrinidae, Barrandeocrinidae, Calypto- 

 crinidae. 



Sub-order II. Reticulata. 

 Family — Crotalocrinidae. 



Order II. Inadunata. 



Crinoids in which the arms are free from the first radials. The calyx 

 generally has an anal side, and frequently a dicyclic base. Interradials 

 may or may not be present. The mouth may be concealed beneath an 

 oral pyramid, or in the centre of a plated disc with open ambulacra. 



Sub-order I. Larviformia. — Interradial and anal plates rarely 

 present. Base monocyclic : arms uniserial. Ambulacra closed, and 

 mouth concealed by an oral pyramid. 



