44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



2.- Side- and covering-plates rudimentary. 



Bathymetric Thermal 



range range 



Pentacrinitidae (except Calometri- 



cke, Thalassometridae, Charito- 



metridse, and Pentacrinitida) . . . 0-2900 28.7-80.0 



Phrynocrinidce 508-703 38.1-40.0 



Side- and covering-plates, in one form or another, are of almost 

 universal occurrence among the earlier crinoids. 



In certain of the later and more, specialized types the development 

 of the plates has been more or less completely suppressed. 



In this we see a clear example of specialization through suppression 

 of a fundamental structure. 



Frequency at different depths Frequency at different temperatures 



Degrees 

 Fathoms 1 2 Fahrenheit 1 2 



O-IOO 2 I 80-75 I I 



I00-2OO 2 I 75-70 2 I 



200-300 3 I 70-65 2 I 



300-400 3 I 65-60 2 1 



400-500 3 I 60-55 2 1 



500-6OO 4 2 55-50 2 1 



60O-7OO 4 2 50-45 2 I- 



700-800 4 2 45-40 3 I 



800-900 4' I 40-35 4 2 



900-1000 4 1 35-30 3 1 



1000-1500 3 ! 30-25 1 * 



1500-2000 3 1 



2000-3000 2 I 



1 2 



Average depth 794 fathoms 77% fathoms 



Average temperature 50.0 Fahr. 51.2 Fahr. 



I. All of the pinnules beyond the oral provided with ambulacral 



grOOVeS. Bathymetric Thermal 



range range 



Pentacrinitidse (except Comasteri- 



dse and Charitometridse) 0-2900 28.7-80.0 



Apiocrinidce 565-940 36.7-38.1 



Phrynocrinidee 508-703 38.1-40.0 ■ 



Bourgueticrinidse 62-2690 29.1-70.75 



Holopodidse 5-120 71.0 



Plicatocrinidce 266-2575 31. 1-43.9 



