254 PROCEEDINGS OF THE ACADEMY OP [1879. 



strong, tapering upward, the tips infolding; composed of single 

 joints. Pinnulae unknown. In most of the genera, the arms lie 

 side by side touching laterally, so as to form with the calyx an 

 apparently compact wall. Radial and arm plates frequently have 

 undulating sutures or additional patelloid plates. The radials up 

 to the second or even the third order form a part of the body, 

 being connected laterally either by a sort of squamous integument, 

 composed of very minute, irregular plates, or by distinct inter- 

 radial and axillary plates, the former varying in number from one 

 to thirty or more, the anal area containing frequently a few addi- 

 tional plates. Anus unknown, except in Taxocrinus and Onycho- 

 crinus, which have a small lateral tube. Ventral disc rarely pre- 

 served; composed of a more or less soft or scaly integument, 

 yielding to motion in the bod\ r and arms. 



This family might very appropriately be called the Articulates 

 of the Paleozoic Crinoids, being especiall}' distinguished in most 

 of its species by a peculiarity of structure which prevails through- 

 out the rays and arms. The plates have rather shallow excava- 

 tions on their outer upper margins, corresponding to projections 

 on the lower edge of the succeeding plates, which sometimes take 

 the form of superficial patelloid plates, independently articulated, 

 and sometimes anchylosed with the margin of the plate above. 

 This feature produces what seems to be an articulate structure in 

 the whole skeleton, and indicates that the body as well as the arms 

 was somewhat flexible. The interradial areas are sometimes found 

 depressed and in other cases distended, showing that there had 

 been some expansion or contraction of the body walls due to the 

 mobility of the radial parts, and indicating likewise flexibility in 

 the vault. This feature, which is found so far as we know, in no 

 other family, together with the fact that in most of the genera a 

 ventral covering has never been found preserved, leads us to infer 

 that this portion of the body was more or less composed of rather 

 fragile perhaps scaly material, instead of solid plates. If these 

 Crinoids had been provided with a rigid dome, the little projections 

 along the radial and arm plates would have interfered with the 

 spreading of the arms, which is rather facilitated by the mobility 

 of the dorsal side, and the pliant nature of the vault. Such motions 

 would be likewise aided by the patelloid plates, which are gener- 

 ally found in large species, and in those in which the interradial 

 spaces are comparatively rigid. 



