CRINOIDEA. 



273 



calyx is somewhat globular, consisting of five " basals," alter- 

 nating with an equal number of "parabasals" or "sub- 

 radials," these in turn being followed by the " radials." 

 There are generally three " radials " to each arm, the primary 

 radials being comparatively large, while the other ones are 

 small. There are no " inter-radials." The structure of the 

 upper surface of the calyx in this genus has not yet been 

 completely made out. The vault of the calyx is always 

 slightly arched, or comparatively flat and depressed, and 

 there appears to be a small anal proboscis on one side. A 

 central mouth has been described as present ; but specimens 

 examined by Meek and Worthen 

 would go to show that the ap- 

 parent mouth is due to breakage, 

 and that the summit of the calyx 

 is really vaulted over by calcare- 

 ous plates, the mouth, as in the 

 Palseocrinoids generally, being thus 

 hidden from view. The genus 

 CyatJiocrinus is mainly confined 

 to the Carboniferous and Permian 

 rocks, though examples have been 

 described from both the Silurian 

 and Devonian. The Carboniferous 

 genus Zeacrinus is also related to 

 CyatJiocrinus, but the basals are 

 very small, and there are four, 

 six, 01- more anal plates. We may 

 place here also the curious Icktliyo- 

 crinus of the Silurian and Car- 

 boniferous (fig. 162, &), the arms 

 of which are frequently bifurcated. 

 Allied to the preceding is the 



Fig. 160. Calyx and part of the 



family Of the PoteriOCmnidce, Of arms of Poteriocrinus radiatus, show- 

 -, . -, T-, , . . ,, ing the proboscis. Carboniferous. 



Which PoteriOCnnUS IS the type. (After De Koninck and Le Hon.) 



In this genus (fig. 160) the cup 



consists, as in CyatJwcrinus, of five basals, five parabasals, 

 and a variable number of radials, the primary radials being 

 the largest ; and there are no inter-radials. There are, 

 VOL. I. s 



