1881 ] NATURAL SCIENCES OF PHILADELPHIA. 35t 



b. Gh/ptasterites. — Calyx turbinate, symmetry bilateral, radials 

 legs carinated than in the preceding group. A special anal plate 

 supported upon the basals, with another within the second series, 

 resting between the two inten-adials, and in line with the first 

 interradial plate of the four lateral areae. Upper Silurian. 



c. Rhodocrinites — Cal3'^x subglobose, somewhat depressed ; sym- 

 metry nearly perfectly pentahedral. Radials without elevated 

 ridges. Interradial plates extending down to the basals, posterior 

 area but little distinct from the others, sometimes a little wider, 

 with one or two irregular additional plates. Pound from the 

 Upper Silurian to the Subcarboniferous. 



These groups, as those of the Actinocrinidae, are based upon 

 the general form of the body and the arrangement of anal plates. 

 In their form, the Glyjjtocrinites resemble the Glyj^tasterites^ but 

 in the arrangement and position of interradial and radial plates 

 the former agree with the Rhodocrinites. It might have been 

 not out of the way if we had placed the genus Glyptocrinus in a 

 group by itself, as it differs from Ai-chseocrinus and Reteoci-inus^ 

 with which it has been associated, and from all other Rhodocrinidse, 

 in having the first plate at each interradial side placed between 

 the second radials, a combination which is found not unfrequently 

 in the earlier Actinocrinidie. This becomes more important since 

 some species of that genus apparently have no underbasals, and 

 it is a question whether that genus, at least partly, should 

 not be arranged with the other group altogether. The unmis- 

 takable evidence of minute underbasals in some species, and the 

 close aflSnities which the genus has with Reteocrinus^ with which 

 it is connected by most remarkable transition forms, has induced 

 us to place it with the Rhodocrinidae. Glyptocrinus evidently 

 forms a link between those two great divisions, and leans as much 

 to the one as to the other, but whether it is the prototype of the 

 Actinocrinidai or of the Rhodocrinidoe we are unable to assert, 

 there being arguments in favor of both theories. It seems to us 

 more probable that the Rhodocrinidse were introduced first, but 

 this must remain a supposition so long as we know comparatively 

 nothing of the crinoidal forms which preceded Glyptocrinus. 



The arms of the Rhodocrinidse in the Lower Silurian, are single- 

 or double-jointed ; the Upper Silurian forms, almost without excep- 

 tion, have two rows of interlocking plates. Respiratory pores, such 

 as noticed in the Actinocrinidse, have never been observed in this 



