20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



crinoid ") type of column by a difference in the direction of the 

 long axes of the ellipses at either end of each columnal whereby 

 the column as a whole forms a series of spirals. 



The bourgueticrinoid type of column, with its relatively few 

 columnals, each of the minimum volume compatible with the neces- 

 sary rigidity, is a good instance of specialization through the gradual 

 suppression of the skeleton forming power of the animal. 



Frequency at different depths Frequency at different temperatures 



, «• * r * -^ 



Degrees 

 Fathoms 1 2 Fahrenheit 1 2 



0-100 3 80-75 O I 



100-200 3 75-70 o 3 



200-300 I 2 . 70-65 2 



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



4OO-5OO I 2 60-55 O 2 



500-600 I 4 55-50 2 



600-700 i 4 50-45 2 



700-800 I 4 45-40 I 2 



800-900 1 3 40-35 1 4 



900-1000 1 3 35-30 1 2 



1000-1500 1 2 30-25 , 02 



1500-2000 1 2 



2000-3000 1 2 



1 2 



Average depth 936 fathoms 747 fathoms 



Average temperature 37-5° Fahr. 51.0 Fahr. 



1. Column composed of a single type of columnals, without a 



proximak Or nodals. Bathymetric Thermal 



range range 



Plicatocrinidae 266-2575 31. 1-43.9 



Apiocrinidse (Carp enter ocrinns) . . .565 38.1 



2. Column including modified columnals, a proximale or nodals. 



Bathymetric Thermal 



range range 



Pentacrinitidse 0-2900 28.7-80.0 



Apiocrinidse (Proisocrinus) 940 36.7 



Phrynocrinidse 508-703 38.1-40.0 



Bourgueticrinidse 62-2690 29.1-70.75 



In the primitive crinoids, and in the very young (phytocrinoid 

 stage) of the comatulids, the column is composed of an indefinite 

 number of similar ossicles, which continuously increases during the 

 life of the individual. 



In the Articulata, however, the column typically, after attaining 

 a certain definite number of columnals and reaching a certain definite 

 length, abruptly ceases further growth, and the topmost columnal 

 becomes attached to the calyx by close suture, developing into what 

 is, to all intents and purposes, an apical calyx plate, the so-called 



