2*74 CR1NOIDEA. 



however, four to six anal plates ; and the upper surface of 

 the calyx, instead of being depressed, is always swollen and 

 convex, and furnished with a very large anal tube or " pro- 

 boscis." The genus (with various sub-genera) commences in 

 the Silurian, is present in the Devonian, and abounds in the 

 Carboniferous period, after which it disappears. If the Car- 

 boniferous genus Zeacrinus be proved to have a large pro- 

 boscis, it will have to be removed from the Cyathocrinidce 

 and placed here. The Silurian genus Dendrocrinus also stands 

 very close to Poteriocrinus, and possesses a greatly- developed 

 proboscis, in some species of extraordinary length. 



In the little group of the Rhodocrinidce, typified by the 

 Carboniferous genus Rliodocrinus (fig. 161) there are five basals 



Fig. 161. Diagram of the dissected calyx of Rhodocriints (after Schultze). b, Basals ; 

 p, Parabasals ; r, First radials ; i, Inter-radials ; a, Anal plates. 



and five parabasa]s or sub-radials ; there are three cycles of 

 radial plates ; there are from six to eight " inter-radials " in 

 each inter-radial space ; the anal plates are eight to twelve 

 in number ; and the arms, varying in number from ten to 

 twenty, are bifurcated two or three times during their course. 

 Very nearly allied to likodocrinus, though apparently separ- 

 able from it, is the Carboniferous genus Gilbcrtsocrimis. 



