NO. IO PHYLOGENETIC STUDY OF RECENT CRINOIDS CLARK 



27 



2. All five orals of the same size. 



Bathymetric Thermal 



range range 



Pentacrinitidse 0-2900 28.7-80.0 



Holopodidae 5-120 71.0 



In the older crinoids, in which as a rule the posterior interradius 

 was enlarged and modified by the inclusion of plates not occurring 

 in the other interradii, the posterior oral was as a rule larger than 

 the other four. 



In the later types which, through the suppression of features 

 causing the differentiation of the anal interradius, exhibit a very 

 nearly perfect pentamerous symmetry, the orals are commonly all of 

 the same size. 



The similarity of the orals is always associated with, and is an 

 index of, a suppression of certain constituent parts of the original 

 calyx structure, and is almost invariably associated with a reduction 

 in the size of the orals themselves. 



Frequency at different depths 



Frequency at different temperatures 



