162 SIDNEY F. HAEMEB. 



distinguish between a colony of C. aculeata without spines 

 and a small variety of C. ramosa unless ovicells are present. 



C. ramosa further appears to me to be much the most 

 variable of all the species I have examined, while C. eburnea, 

 and, next to this, C. denticulata, are the least variable. The 

 greater variability of C. ramosa comes out perfectly clearly by 

 subtracting the minimum from the maximum measurements 

 given in the table, and comparing together the results thus 

 obtained for the diflFerent species. If this be done for D — J, it 

 will be found that, in every case except F (in which the limits 

 are the same for C. ramosa and C. denticulata), the greater 

 variability of C. ramosa comes out, and usually with striking 

 distinctness. 



It will be noticed that the largest variations are in the length 

 of the zooecia, and, correlated with this, in the size of the 

 ovicells. But though the ovicells are thus by no means exempt 

 from variation, their principal specific character (the shape of 

 their aperture) is retained throughout without material alte- 

 ration. 



The fact that a colony of C. eburnea, on which some 

 unusually small ovicells were present, has been taken into 

 account in the table, makes these structures appear much 

 more variable than they are in normal cases. 



