CYSTOIDEA. 



287 



lower extremity is composed of a single, long, spindle-shaped 

 piece. There are also forms in which the mode of attach- 

 ment of the body is still unknown. The calyx consists of a 

 a number of polygonal calcareous plates accurately fitted 

 together, and enclosing all the viscera of the animal. Some- 

 times the plates are indefinite in number and arrangement ; 

 but in other cases the number of plates is limited, and they 

 are arranged according to a definite plan. In other cases the 

 number and arrangement of the plates may be definite on 

 one side of the calyx and indefinite on the other. 



As regards the structure of the arms of the Cystideans, 

 there is a good deal of diversity. In some forms there were 



Fig. 172. Cystideans. A, Caryocrinus ornatua: a, Column; b. Calyx; c, Scars where 

 pinnulse were attached ; d, Valvular pyramid. B, Pleurocystites squamosus (dorsal side) : 

 p, p, Two of the pectinated rhombs, c, Pseudocrinus bifasciatiis. D, Lepadocrinus Gebhardi. 



no true arms, comparable with the arms of the Crinoids ; but 

 there were small jointed processes, which were attached to 

 the calyx, and which represent the " pinnulse " or lateral 

 branches of the arms of the Grinoids. In some cases, grooves 

 corresponding with the brachial grooves of the Crinoids 

 are seen to extend from the point of attachment of each 

 pinnula to the summit of the calyx. In other cases, as in 



