CRINOIDEA. 



275 



All the preceding families are provided with a zone of 

 " parabasal " or " sub-radial " plates, and if we regard this 

 character as being of high classificatory value, we must con- 

 sider here the groups of the Taxocrinidce and Anthocrinidce, 

 both of which in some respects differ widely from the typical 

 Palasocrinoids. In the Taxocrinidce, typified by the genus 

 Taxocrinus (fig. 162, c) of the Silurian, Devonian, and Carbon- 



Fig. 162. Upper Silurian Cfinoids. a, Calyx and arms of Eucalyptocrinus polydactylus, 

 Wenlock Limestone; b, Ichthyocrimis Icevis, Niagara Limestone, America; c, Taxocrinus 

 tuberculatus, Wenlock Limestone. (After M'Coy and Hall.) 



iferous deposits, there are three very small basals, succeeded 

 by five large sub-radial or parabasal pieces, which support 

 from three to seven cycles of radials. The inter-radials may 

 be wanting, and are always few in number. The discovery 

 that Forbesiocrinus, of the Devonian and Carboniferous, really 

 possesses three minute basals (not represented in fig. 158, 

 after De Koninck and Le Hon, in which the plates lettered 

 b thus really are the " parabasals "), places this genus in the 

 immediate neighbourhood of Taxocrinus, from which it is 

 only separated by the possession of numerous inter-radial 

 and anal plates. Taxocrinus is remarkable, as compared 

 with almost all the Palseocrinoids, in apparently having the 

 upper surface of the calyx covered by soft integument only, 

 ^instead of being vaulted over with calcareous plates. 



