NO. 



10 PHYLOGENETIC STUDY OF RECENT CRIN01DS CLARK 



29 



Frequency at different depths 



Fathoms 

 O-IOO 



100-200 



20O-30O 



3OO-4OO 



4OO-50O 



50O-60O 



60O-7OO 



700-800 



80O-9OO 



900-IO00 

 IOOO-150O 

 I500-200O 

 2OOO-3OOO 



Average depth 



Frequency at different temperatures 



Degrees 



Fahrenheit 



80-75 

 75-70 

 70-65 

 65-60 

 60-55 



S5-6o 

 5o-45 

 45-40 

 40-35 

 35-30 

 30-2.5 



596 fathoms 



Average temperature | ^_o° J Fahr. 



1. Mouth central. Bathymetric 



range 

 Pentacrinitidas (except Comasteri- 

 dse, and the five largest genera of 



Heliometrinae) 0-2900 



Phrynocrinidae 5°8-703 



Bourgueticrinidae 62-2690 



Holopodidae 5-120 



Plicatocrinidae 266-2575 



2. Mouth more or less excentric. 



Bathymetric 

 range 



Pentacrinitidse (Comasteridse, and 



the five largest genera of Helio- 



metrinse) 0-1062 



808 fathoms 

 52.9° Fahr. 



Thermal 

 range 



28.7-80.O 



38.I-4O.O 



29.I-7O.75 



7I.O 



3 1. 1-43-9 



Thermal 

 range 



28.7-80.O 



One of the most invariable features of crinoidal structure, a neces- 

 sary corollary of the primitive and fundamental pentamerous sym- 

 metry of these animals, is the central position of the mouth upon 

 the disk. 



Only in a very few types, and in these only very late in the 

 ontogeny, do we find the mouth in an excentric position. 



The migration of the mouth to an excentric position indicates a 

 high degree of specialization which, like many similar features, is 

 of more or less sporadic occurrence. The migration of the mouth 

 toward an excentric position indicates the gradual suppression of the 

 primitive and fundamental pentamerous symmetry of the crinoids. 



