324 MigheW Catalogue of 



N. antiqua, (fossil,) Migh. This is found, sparingly, in 

 company with the preceding species. 



N. dtlphinodonta, Migh. I am not aware that this species 

 has been found anywhere but in Casco Bay. In the spring 

 of 1841, I found it for the first time plenty, subsequently it 

 has been rarely seen. 



N. cascdensis, Migh. Hab. Casco Bay. T detected a single 

 fine specimen of this species in the spring of 1840. 



N. porflandica, (fossil,) Hitchcock. This species occurs 

 somewhat plentifully at Westbrook. I have also received it 

 from Saco, and Brunswick, and am informed that it occurs at 

 Gardiner. The geological formation is identical at all the lo- 

 calities. 



Genus Unio. Brug. 



U. complanatus, Soland. This variable species occurs in 

 very great abundance in this State. In small collections of 

 still water where the bottom is muddy, it attains the greatest 

 magnitude and perfection. It sometimes occurs in running 

 w^ater, in pebbly beds, where it is observed to be much com- 

 pressed, distorted, and eroded. In open lakes, in sandy 

 beds, it is usually diminutive, and much compressed. 



U. radiatus, Gmel. Barnes. This species is plenty at some 

 localities, but is far less common than the preceding. A va- 

 riety! is occasionally found, which differs so much from the 

 common type that I have supposed it must be the siliquoideus 

 of Barnes. Recent observations, however, would seem to 

 show that the specific distinctions between radiatus and sili- 

 quoideus are by no means definitely settled. I therefore pre- 

 fer to regard it at present as a mere variety of radiatus. Pro- 

 fessor Adams remarks, that he is at a loss in distinguishing 

 between Vermont specimens of U. siliquoideus and U. radia- 

 tus. However this may be, there is no difficulty in discover- 

 ing the difference between what he regards as siliquoideus of 

 Vermont, and what I regard as radiatus of Maine. 



U. ochraceus, Say. This species occurs in the Kennebeck 

 river. Rare. 



