138 



Family BISSOIDAE. 



BYTHINELLA, Moq-Tand. 



B. obtiisa; Lea. Lewis. Thia species may Lave been noticed 



by Robinson under a different name, clearly 

 not tenable. 



GILLIAj Stimjison. 



G. altiliSj Lea. Catalogued by Aldrich as Somatocjynis integer. 



Say. 



SOMATOGYRUS, QUI 



S. subg'lobosus^ Say. Lewis ; Robinson. Usually called S. isogonus, 



Say. 



AMNICOLA,^^ Gould and Raldeman. 



A. porata, Say. Cayuga Lake (Say). 



A. pallida, Raid. l^ake Champlain (Haldeman). 



A. CinciunatiensiSj Anth. Lewis. Recorded by Robinson under another 



name ? 



A. oii)iciilata, Lea. Cayuga Lake (Lea). 



A. liisti'icaj Say. Cayuga Lake (Say) ; Central New York (Lewis). 



A. liiuosa. Say. Delaware River? Southern New York? 



15 The genus Amnicola seems to have been a source of much difficulty to the students of 

 Ameiiciin Conchology, and is even yet apparently not well understood. Dr. Gould in his Inv<.-r- 

 tebrata of Massachusetts (original edition) seems to have made a tolerable approach to the 

 identification of Say's ^JWrtto. Forms precisely like Massachusetts shells from localities pro- 

 ducing shells studied by Dr. Gould, found in various lakes and streams in the State of New 

 York, show that identical species in this genus are wide-spread. The occurrence of two fomis 

 in Cayuga Lake, both described and located by Say ; and the simultaneous occurrence of two 

 forms (meeting Say's text in all but the locality) in numerous small bodies of w.atcr within the 

 State of New York, must be regarded as throwing very strong light on questions of identity. 

 The only safe inference that can be drawn from the considerations above stated is, that 2)allida 

 and orHculata Ai-p. probably varieties of porata. As regards pallida (referred to Lake Cham- 

 plain), we find it jrt'obably associated with a shell which Adams in his "Vermont Shells" 

 correctly identifies as Say's lustrica. If this probability should e\entually prove to be cer- 

 tainty, it will allbrd abundant corroboration of all that is inferred from the association and 

 distribution, of species elsewhere. If, on tlie other hand, it should prove to be true that the shell 

 Adams identified as lustrica was not really that species, we can then infer no less than that the 

 shell he had before him was identical with the species now known as Btjthinclla obtiisa. Lea. 



