NO. IO PHYLOGENETIC STUDY OF RECENT CRINOIDS CLARK 



45 



2. Some or all of the pinnules on certain arms without ambulacral 



grooves. 



Bathymetric 

 range 



Pentacrinitidae (Comasteridae, 

 Charitometridae) 0-1200 



Thermal 

 range 



3Q.5-80.0 



Primarily all the pinnules on a crinoid arm are similar, and all are 

 provided with ambulacral grooves. In many of the later types, 

 however, the ambulacral grooves on the proximal pinnules have been 

 suppressed. 



In other late types not only have the ambulacral furrows and asso- 

 ciated structures been suppressed on the proximal pinnules, but also 

 they have disappeared from the genital, and in many cases from all, 

 the pinnules. 



The disappearance of the ambulacral grooves and associated struc- 

 tures from the genital and distal pinnules is an instance of specializa- 

 tion through suppression of a fundamental structure. 



Frequency at different depths 



Frequency at different temperatures 



VI. GENERAL 



I. Skeleton composed of more than a million ossicles. 



Bathymetric 

 range 

 Pentacrinitidae (part of Capillaste- 

 rinae, Comasterinae, Zygometridae, 

 Himerometridae, Mariametridse, 

 Colobometridas, and Heliometri- 

 nae, and Pentacrinitida) 0-1350 



Thermal 

 range 



28.7-80.O 



