122 



T1IK NA UTII.US. 



convinced thai Lea's bicarinata is not the hicarinate form of Say's 

 tricarinata, but is a distinct species, which also has a tricarinate 

 form. I have the typical form of V. bicarinata from Columbia and 

 Philadelphia, Pa., and Port Oram, N. J., and the tricarinate form 

 from Muscatine, la., and Utica, III. Withjn the last few weeks I 

 have had occasion to examine critically hundreds of specimens of V- 



v. 



tricarinata in its various aspects [from Michigan, and a considerable 

 number from at least ten different states and Canada, and I have yet 

 to see the first specimen that in any way seems to connect the two. 



In comparison with V- tricarinata, Lea's species is larger, dis- 

 coidal ; the upper surface of the whorls slopes downwards from the 

 carina to the suture, giving a concave appearance to the upper surface 



