40 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



tion through the suppression of one of the most fundamental elements 

 of the arm structure. 



Frequency at different depths 



Fathoms 



O-IOO 



100-200 



200-300 



3OO-4OO 



4OO-5OO 



SOO-60O 



60O-7OO 



700-8OO 



80O-9OO 



900-IOOO 



I 000-1500 



1500-2000 



2000-3000 



Frequency at different temperatures 



Degrees 

 Fahrenheit 



8o-7S 

 75-70 

 70-65 

 65-60 

 60-55 

 55-50 

 5o-45 

 45-40 

 40-35 

 35-3o 

 30-25 



Average depth 723 fathoms 



Average temperature 42.9 Fahr. 



V. PINNULES 



1. Pinnules, at least the proximal, more or less sharply triangular 



in croSS Section. Bathymetric Thermal 



range range 



Pentacrinitidae (except Macrophre- 



ata) . 0-1600 34.2-80.0 



Apiocrinidse 565-940 36.7-38.1 



Phrynocrinidae 508-703 38.1-40.0 



Bourgueticrinidas 62-2690 29.1-70.75 



Holopodidae 5-120 71.0 



Plicatocrinidas 266-2575 31. 1-43.9 



2. Pinnules circular or elliptical in cross section. 



Bathymetric Thermal 



range range 



Pentacrinitidae (Macrophreata) ... 0-2900 28.7-79.1 



In all of the earlier crinoids in which the structure of the pinnules 

 can be made out these organs are found to be prismatic in form and 

 more or less sharply triangular in cross section, the ambulacral 

 groove occupying a side opposite to a sharp (dorsal) ridge. 



In a few highly specialized types the pinnules, instead of being 

 strongly prismatic and triangular in cross section, are more or less 

 cylindrical and circular or elliptical in cross section, with very slender 

 segments and swollen joints. 



In the change from the prismatic to the cylindrical type the pinnules 

 lose a very large part of the calcareous substance, becoming very 



