C1UN01DEA. 2.79 



the Crinoid, since the lip of its shell has closely adapted its 

 form to that of the surface to which it is attached. We may 

 therefore safely accept the conclusions reached by these 

 observers, that the Platyceras was in the habit of attaching 

 itself parasitically to the side or summit of the proboscis of 

 Platycrinus and other Crinoids, thus obtaining a share of the 

 minute animalcules upon which its host lived. 



Platycrinus is essentially a Carboniferous genus, though 

 forms certainly not more than sub-generically differing from 

 it occur in the Upper Silurian and Devonian. The De- 

 vonian genus Hexacrinus is very closely allied to Platycrinus, 

 but it possesses one large anal plate, which rests directly 

 upon the basals (as in Actinocrimis). In Coccocrinus, of the 

 Upper Silurian and Devonian, we have an aberrant type of 

 this family, in which the summit of the calyx is covered by 

 five large pentagonal plates, forming a depressed pyramid. 



In the extraordinary family of the Eucalyptocrinidce is 

 only the abnormal Eucalyptocrinus (Hypanthocrinus) of the 



Fig. 160. A, Calyx and arms of Eucalyptocrinus rosaceiis, viewed from one side, of the 

 natural size Devonian (after Schultze) ; B, Calyx of Glyptocrinus bctsalis, viewed from one 

 side, of the natural size Lower Silurian (after M'Coy). 



Silurian and Devonian (figs. 162, a, and 166, A). In this 

 genus the calyx is inverted upon itself, the calicine cup 

 being deeply concave at its base, so as to look like the 

 bottom of a wine -bottle. As now known, there are four 

 small basals (as in Melocrinus), which carry five large 

 primary radials. These are strongly bent, one half of each 

 passing up into the basal funnel, while the other half ap- 



