32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



Frequency at different depths Frequency at different temperatures 



Degrees 

 Fathoms 1 2 Fahrenheit 1 2 



0-100 3 80-75 O I 



100-200 i 3 75-70 O 3 



200-300 2 2 70-65 O 2 



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



400-500 2 3 60-55 I 2 



500-6OO 2 5 55-50 I 2 



600-700 2 5 50-45 I 2 



700-800 2 5 45-40 2 3 



80O-9OO 2 3 40-35 2 5 



90O-IO00 2 3 35-30 2 2 



IOO0-I50O 2 2 30-25 2 



I500-2000 2 2 



2000-3000 I 2 



1 2 



Average depth 795 fathoms 723 fathoms 



Average temperature 37.0 Fahr. 42.9 Fahr. 



1. Arms with IBr series in which the outer element is axillary. 



Bathymetric Thermal 



range range 



Pentacrinitidse (except Eudiocrinus 



and Metacrinus) 0-2900 28.7-80.0 



Apiocrinidae 565-940 36.7-38.1 



Botirgueticrinidce (Ilycrinus, Bathy- 



crinus, Monachocrinus) 743-2690 30.9-40.0 



Holopodidse 5-120 71.0 



2. Arms with IBr series in which the outer element is not axillary. 



Bathymetric Thermal 



range range 



Pentacrinitidae (Eudiocrinus and 



Metacrinus) 22-630 39-5-71-0 



Bourgueticrinidae (Dcmocrinus, By- 



thocrinus, Rhizocrinus) . 61-1300 31.8-48.7 



In the course of the development of the IBr series it came about 

 that the outer element (the IBr,) is normally axillary, bearing two 

 exactly similar arms instead of a single arm as in the case of an 

 arm-bearing radial. 



Occasionally it happens that the IBr 2 is not axillary, but gives 

 rise to a linear series of ossicles, like the primitive radial. A more 

 or less common meristic variation in many diverse types, this feature 

 has in others become fixed and invariable. 



The reduction of the IBr 2 from its normal condition of an axillary 

 to an ossicle giving rise to a simple linear series of ossicles, with the 



