138 



Faniilv RISSOIDAE. 



BYTJIINELLA, Moq-Tand. 



B. obtllSDj Lea. Lewis. This Hi)ficif;H may liavc; bofii notic<;d 



by IloVjinson under a dillerent name, clearly 

 not tenable. 



(« I LLI A J Stimpson. 



(». altiliSj Lea. Catalogued by Aldricli as So?natof/yru8 integer. 



Say. 



SOMATOGYRUS, Gill. 



S. SUbg'lobo.SUSj Soy. Lewis; Robinson. U.sually called S. isogonus, 



Say. 



AMNICOLA,^^ Gould and Ilaldemnn. 



A. porata, Saij. Cayiiga Lake (Say). 



A. pallida^ Ilald. l^ake Chaniplain (Haldeman). 



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



name ? 



A. orbiculata, Lea. Cayuga Lake (Lea). 



A. Inst ricaj Say. Cayuga Lake (Say) ; Central Xew York (Lewis). 



A. liinosa^ Say. Delaware River ? Soutliern New York ? 



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

 American Conchology, and is even yet apparently not well understood. Dr. Gould in his Invi-r- 

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

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

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

 York, show that identical species in this genus are *ide-spread. The occurrence of hvo forms 

 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 water 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 tlie considerations above stated is, that jxillida 

 and 07-bicidata arf. probably varieties of jwrata. As res^ards pallida (referred to Lake Cham- 

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

 correctly ideatifles as Say's lustrica. If this probability should eventually prove to be cer- 

 tainty, it will 'afford abundant corroboration of all that is inferred from the association aud 

 distribution of species elsewhere. If, on the 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 Bijthinella obiusa. Lea. 



