NO. IO PHYLOGENETIC STUDY OF RECENT CRINOIDS— CLARK 



37 



But in the more specialized types and in the fully grown comatulids 

 the reduction in size of the calyx and its retreat toward the dorsal 

 pole causes the arms, which always remain of approximately the same 

 relative proportions, gradually to come to occupy the entire distal 

 border of the radials. 



The occupation by the arm bases of the entire distal border of the 

 radials is an indication of the reduction in size of the radials and other 

 calyx plates, and hence must be regarded as indicating specialization 

 through suppression or atrophy of the skeletal structures. 



Frequency at different depths Frequency at different temperatures 



Degrees 

 Fathoms 1 2 Fahrenheit 1 2 



o-ioo i 3 So-75 I I 



I00-2OO I 3 75-70 I 3 



200-300 2 2 70-65 I 2 



3OO-4OO 2 2 65-60 I 2 



40O-5O0 I 2 60-55 I 2 



500-6OO I 4 55-50 I 2 



6OO-700 I 4 50-45 2 



7OO-800 I 4 45-40 I 2 



80O-9OO I 3 40-35 I 4 



9OO-IOOO I 3 35-30 I 2 



I00O-I5O0 I 2 30-25 O 2 



I50O-2OOO I 2 



2O00-3000 I 2 



1 2 



Average depth 612 fathoms 747 fathoms 



Average temperature ."..-< g-'^o fFahr. 51.0 Fahr. 



1. All the arms of equal length. Dl , ,. „, . 



t- & Bathymetric Thermal 



range range 



Pentacrinitidae (except Comasteri- 



dae) 0-2900 28.7-80.0 



Apiocrinidae 565-940 36.7-38.1 



Phrynocrinidae 508-703 38.1-40.0 



Bourgueticrinidae 62-2690 29.1-70.75 



Plicatocrinidse 266-2575 31. 1-43.9 



2. The posterior arms dwarfed. „ .. ™ ' 



c Bathymetric 1 hernial 



range range 



Pentacrinitidae (Comasteridae) .... 0-830 44.5-80.0 



Holopodidse 5-120 71.0 



The crinoids being primarily and fundamentally pentamerous, all 

 five of their arms (or groups of arms) are primarily of equal size 

 and length. 



