NO. IO PHYLOGENETIC STUDY OF RECENT CRINOIDS CLARK 



35 



whereby the original fibers have been collected and compressed into 

 compact bundles, and is therefore an indication of development by 

 suppression of the skeleton forming power. 



Frequency at different depths 



Fathoms 



O-IOO 



100-200 



2OO-3OO 



3OO-4OO 



4OO-SOO 



SOO-600 



600-700 



700-800 



800-900 



900-1000 



IOOO-150O 



I500-2OOO 



2000-3000 



Frequency at different temperatures 



, A , 



Degrees 

 Fahrenheit 



80-75 

 75-70 

 70-65 

 65-60 

 60-55 

 55-50 

 50-45 

 45-40 

 40-35 

 35-30 

 30-25 



Average depth 



Average temperature 



740 fathoms 

 51.3 Fahr. 



755 fathoms 

 51.6° Fahr. 



i. Division series composed of an irregular number of ossicles. 



Bathymetric Thermal 

 range range 



Pentacrinitidae (Metacrinus, Isocri- 



nus) 5-667 39-5-71-0 



Phrynocrinidae 508-703 38.1-40.0 



Plicatocrinidse 266-2575 31. 1-43.9 



2. All of the division series composed of a fixed number of seg- 



ments - Bathymetric 



range 



Pentacrinitidae (except Metacrinus and Iso- 



crinus) 0-2900 



Apiocrinidse 565-940 



Bourgueticrinidse 62-2690 



Holopodidse 5-120 



Thermal 

 range 



28.7-80.O 

 36.7-38.I 

 29.I-70.75 

 71.0 



Like the first division series, the succeeding division series in the 

 more primitive crinoid types were composed of a variable and irregu- 

 lar number of ossicles. 



After the evolution of the IBr system, of two ossicles only, inter- 

 polated between the radials and the arm bases, this system, as the 

 calyx continued to decrease in size, became developed and extended 

 so as to supplant all of the succeeding division series. 



