MONOGRAPH OF THE EXISTING CRINOIDS. 



265 



metra, Mariameira, Colohometra, Calometra, and the genera of the Perometrinse and 

 of tlie Zenometrina\ 



A muddy bottom induces a great lengtliening and straighteiiing of the cirri 

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

 the cin-i collectively come to form a circular base supporting the animal after the 



Fig. 306. 



Kiu. 307. 



Figs. 306-307.— 306, Diagram showikg the relative size and frequency or the arms and cirri in CoMAcmnA echdjop- 

 tera; the cirri are short, and strong and are ad.vpted for grasping arborescent marine organisms. 307, 

 Diagram showing the rel-ative size and frequency of the arms and cirri is rENTAMETRorBiNVS tuberculatts; 



THE CIRRI are SHORT AND NITMEROUS AND ARE ADAPTED FOR GRASPING MARINE ORGANISMS. 



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

 all of the species of TlMumaiocnnus, Pentametrocrinus, Atclecrinus, Compsometra, 

 Iridometra, Leptometra, Psaihi/rometra, Thysanometra, Coccometra, Craspcdometra, 

 and Eudwcrinus; while the tendency is strongly e^ndent in Capilhster graciUcirra, 

 C. tenuicirra, Comatula tenuicirra, Comaster sihogw, AmpVimetra pro]nngua, Oxy- 

 metra tenuicirra and Dichrometra tenuicirra, all of which are very close to other 



-9146°— Bull. 82—15 18 



