272 



CBINOIDEA. 



tesselata would correspond with the Palaeocrinoids, compris- 

 ing all the species known from the Palaeozoic formations. 



The division of the Crinoidea into stalked and free forms 

 is in many respects inapplicable as a basis of zoological 

 classification. There can, however, be no doubt but that 

 the free Crinoids are structurally an advance upon the fixed 

 forms. It is therefore of interest to note that the stalked 

 Crinoids had attained their maximum in the Palaeozoic rocks, 

 and had even commenced to decline before the free Crinoids 

 first made their appearance in the Mesozoic Series. 



In the absence of any satisfactory classification of the 

 Crinoids, it will be sufficient here to briefly consider the 



Fig. 159. A, Diagram, showing the dissected calyx of CyatJwcrinus (after Hall), ft, Basals ; 

 p, Parabasals ; r, Lowest of the three radials (" primary radials ") ; a, Anal plate. B, Calyx 

 and part of the arms of Cyathocrimis planus, of the natural size. Carboniferous. 



leading types and geological range of the more important 

 families of the order. It should be borne in mind, however, 

 that though some of these families are undoubtedly natural 

 assemblages, the same cannot be affirmed of all of them, 

 while there often exist considerable and legitimate doubts 

 as to the true position of many of the genera. 



The family of the Cyathocrinidce, as represented by Cyath- 

 ocrinus itself, presents us with one of the simplest types of 

 the Pedunculate Crinoids. In Cyatliocrinus (fig. 159) the 



