130 



ANNULOIDA. 



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 

 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 " pinnulae " or lateral branches 

 of the arms of the Crinoids. In some cases, grooves cor- 

 responding with the brachial grooves of the Crinoids are 

 seen to extend from the point of attachment of each pinnula 



Fig. 83. Cystideans. A, Caryocrinus ornatus ; a. Column ; *, Calyx ; c. Scars 

 where pinnulae were attached ; d, Valvular pyramid. B, Plturocyi tiles squamosus 

 (dorsal side) ; p, p, Two of the pectinated rhombs. C, Pseudocrinus bifasciatus. D, 

 Lcpadocnnus Gebhardi. 



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

 and Callocystites, arms were present, but they were bent back- 

 wards and immovably soldered down to the surface of the 

 calyx. The arms spring in these cases from the apex of the 

 calyx, and are anchylosed by their dorsal surfaces to the body. 

 On their ventral surfaces the arms are grooved by furrows 

 which clearly correspond with the brachial grooves of the 

 Crinoids, and on each side of these grooves is a row of pin- 

 nulae. In one or two cases there is only a single row of pin- 

 nules, and the arm seems to have been fastened to the calyx 



