36 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 



65 



The substitution of the primitive division series of a variable and 

 irregular number of ossicles by a system made up of units of two 

 ossicles each, resulting in a great diminution in the number of ele- 

 ments necessary to support a given number of ultimate arm branches, 

 is an example of specialization through suppression of superfluous 

 skeletal elements. 



Frequency at different depths Frequency at different temperatures 



Degrees 

 Fathoms 1 2 Fahrenheit 1 2 



0-100 . i 3 80-75 l 



IOO-200 I 3 75-70 I 3 



2O0-300 2 2 70-65 I 2 



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



400-5OO 2 2 60-55 I 2 



500-600 3 3 55-50 1 . 2 



600-700 3 3 50-45 1 2 



700-800 2 3 45-40 2 2 



800-900 1 3 40-35 3 3 



900-1000 1 3 35-30 1 2 



IOOO-I500 I 2 30-25 O 2 



I50O-2OOO I 2 



200O-300O I 2 



1 2 



Average depth 608 fathoms 756 fathoms 



Average temperature 49-1° Fahr. 51.6 Fahr. 



i. The arms occupy only a portio.11 of the distal border of the 



Bathymetric Thermal 



range range 



Pentacrinitidas (certain genera of 



Calometridse) 0-333 52.Q-75-7 



Plicatocrinidse 266-2575 31. 1-43.9 



2. The arms occupy the entire distal border of the radials. 



Bathymetric Thermal 



range range 



Pentacrinitidas (except certain gen- 

 era of Calometridae) 0-2900 28.7-80.0 



Apiocrinidse 565-940 36.7-38.1 



Phrynocrinidae 508-703 38.1-40.0 



Bourgueticrinidse . 62-2600 29.1-70.75 



Holopodidse 5-120 71.0 



In the primitive crinoids and in the young of the comatulids the 

 calyx more or less extensively encloses the visceral mass dorsally 

 and laterally, and the arms occupy only a relatively small part of the 

 distal border of the radials. 



