MUSEUM OF COMPARATIVE ZOOLOGY. 123 



which I have not seen noted elsewhere except by Maynard, that the young 

 shells of Cenon have both palatal and basal denticles in the apertures which in 

 most forms are absorbed later, though in Cerion s. s. they appear, or part of 

 them, to remain permanently present, as shown in the section of C. uva in the 

 accompanying plate. Helix pentodon Mke., appears to have been founded on 

 an immature Cerion in this state. 



It would be a most valuable contribution to the history of modifications in 

 biology if some one would map out and characterize the areas occupied by the 

 various forms of Cerion in the Bahamas. The differences are quite perceptible, 

 and the conditions under which they arise must be relatively simple. All that 

 has hitherto been done is insufficiently exact for the purpose indicated, and the 

 field is a wide one. 



July 18, 1894. 



