MONOGRAPH OF THE EXISTING CRINOIDS. 



265 



metra, Mariametra, Colobometra, Calometra, and the genera of the Perometrinse and 

 of the Zenometrinse. 



A muddy bottom induces a great lengthening and straightening of the cirri 

 as a whole, correlated with a lengthening of all the component segments, so that 

 the cirri collectively come to form a circular base supporting the animal after the 



FIG. 306. 



FIG. 307. 



FIGS. 306-307. 306, DUGRAM SHOWING THE RELATIVE SIZE AND FREQUENCY OF THE ARMS AND CIRRI IN CoMACTTNIA ECHINOP- 

 TERA; THE CIHRI ARE SHORT. AND STRONG AND ARE ADAPTED FOR GRASPING ARBORESCENT MARINE ORGANISMS. 307, 

 DIAGRAM SHOWING THE RELATIVE SIZE AND FREQUENCY OF THE ARMS AND CIRRI IN I'ENTAMETROCTUNUS TUBERCULATUS; 

 THE CIRRI ARE SHORT AND NUMEROUS AND ARE ADAPTED FOR GRASPING MARINE ORGANISMS. 



fashion of a snowshoe (fig. 308, p. 267); this is carried to an extreme in some or 

 all of the species of TJiaumatocrinus, Pentametrocrinus, Atelecrinus, Compsometra, 

 Iridometra, Lcptometra, Psathyrometra, Thysanometra, Coccometra, Craspedometra, 

 and Eudwcrinus; while the tendency is strongly evident in Capillaster gracilicirra, 

 C. tenuicirra, Comaiula. tenuicirra, Comaster sibogse, AmpJi'iinftra propinqua, Oxy- 

 metra tenuicirra and Dicnrometra tenuicirra, ah 1 of which are very close to other 



79146 Bull. 82 15 18 



