May, 1909. 



New Echinoids — Slocom. 



13 



The dimensions of a number of practically perfect specimens are 

 as follows: 



This table shows that this species exhibits great individual vari- 

 ation in a number of characters. Thus the proportion of length to 

 width varies from wider than long to longer than wide ; the proportion 

 of height to length is variable; the height of the periproct varies in 

 proportion to the height of the test; the basal line and the posterior 

 truncation form an angle varying from 73 to 90 and the position of 

 the apical disc varies from central through subcentral to decidedly 

 anterior. The manner in which these variations are combined is 

 so diverse, however, that no well-marked divisions can be made. 

 Taking two extremes of form such as B and L we find B longer than 

 wide, test low, periproct low, posterior angle 75 , apex anterior; in 

 L the length and width are about equal, test high, periproct high, 

 posterior angle 85 , apex central. This combination of characters 

 would seem to be of specific importance, but S is wider than long, 

 test high, periproct low, posterior angle 84 , apex anterior; F longer 

 than wide, test high, periproct low, posterior angle 82 , apex anterior; 

 X longer than wide, test low, periproct low, angle 77 , apex central. 

 Hence it is evident that these variations are not constant but in- 



* Crushed vertically, 

 t Crushed laterally. 



