of London, where I have studied thorn. A duplicate of the latter is 
in the United States National Museum, figure® of it bare given in PI. 
figs. • The difference between P. d % st an s and P. globosa consists 
in the calicos of the former being one-half or more than on e-half the! 
djiameier apart, while ia the latter the distance between them i® usual 
ly less than one-half this diameter. 
Differential characters ; Oyphaetrea hyadeg and C* carlbasa are 
closely related species. The oaliees of the former, however,- are con- 
stantly larger than those of the latter, and the tertiary septa, ex- 
cept occasionally in young co rails, constantly fis® to the sides of 
the secondaries? the latter species has smaller eaiiees* and except 
when the pall are decidedly thickened, ha® the Inner ends of the ter- 
tiary septa free. These difference® are constant in the considerable 
aiites of specimens that I have been able to study. 
