PHYLUM ECHINODERMATA 



209 



Fig. 148. — A crinoid, Pentacrinus maclearanus. Arms and 

 portion of stem. (From the Cambridge Natural History, after 

 Thompson.) 



of the living crinoids are 

 found at moderate 

 depths, a few are deep- 

 sea forms, and some 

 inhabit shallow water. 

 They are often attached 

 by a jointed stalk. 

 Some species break off 

 from the stalk when 

 they become mature, 

 and probably swim 

 about by means of mus- 

 cular contractions of the 

 arms. 



The arms of crinoids 

 are usually five in num- 

 ber. The apparently 

 greater number is due to 

 branching near the base 



outh 



C D 



Fig. 149. — Fossil Echinoderms. A, Theco- 

 cystis saculus (Thecoidea). B, Trochocystis 

 bohemicus (Carpoidea). C, Echinos phcerites 

 aurantium (Cystoidea). D, Granatocrinus 

 (Blastoidea). (A, B, C, from the Cam- 

 bridge Natural History. A and B, after 

 Jackel; C, after Zittel ; D, from Weysse.) 



