340 



BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



This group of species is set apart from other species by the great 

 development of the axial excretory vacuole. All but C. ohovoidea 

 are shaped much like the slender forms of C. dimidiata. Cepedea 

 dbovoidea is flattened in front and, in consequence, is broader in this 



part of the body. Its flattened anterior end separates it a little from 

 the other species, to which, however, it seems related. So far as avail- 

 able evidence goes, it was probably derived from an African member 

 of this group, which migrated to America. Its presence in Florida 

 might seem to suggest a former direct connection between Florida and 



