OF CONCHOLOGY. 59 



some of the waters of the Ohio basin. It would seem from this 

 that Mr. Say did not regard the form so much as he did the 

 accidental circumstances of the molluscs he confounded. 



The presence or absence of calcareous salts in waters inhabited 

 by molluscs is the important influence upon which the perfection 

 of shells depends. This will be apparent to any one who will 

 compare shells found in the soft waters of some of the Atlantic 

 States with shells from the calcareous waters of the Western 

 States. Mr. Say's original decisa inhabits the soft waters of 

 the Atlantic Slope. It is by some innate principle better qualified 

 to live in such waters than some of the species which Mr. Bin- 

 ney confounds with it, and which are found principally in waters 

 highly charged with lime. 



When by chance decisa and other species of Melantho are 

 found inhabiting the same water, it will be observed that decisa 

 is less liable to erosion than its associated species. 



M. decisa has been found in its greatest perfection associated 

 with integra, De Kay, and rufa, Haldeman ; the associated 

 species being almost invariably in some degree eroded, while 

 decisa remains intact. We may infer that in extreme conditions 

 integra and rufa might become extinct under those influences 

 which decisa would survive with the loss of a portion of the 

 apicial whorls. Such appears to be the explanation of the 

 presence of decisa and the absence of other species of Viviparidce 

 in some of the waters of the Atlantic Slope. 



Of. these things, Mr. Binney may be presumed to be un- 

 informed, and the absence of these and other facts may in a 

 measure explain how it happens that in his compilations he 

 allowed his opinions to deviate from the course in which the 

 observer of nature is led. 



For a correct interpretation of Mr. Say's decisa we must refer 

 to the shells of the Atlantic Slope. His integra we do not yet 

 understand, and until some fortunate collector shall present to 

 the world a full series of shells from the original locality of Mr. 

 Say's integra this species will remain an uncertainty. Our 

 ideas of integra are, as yet, simply a reproduction of the 

 opinions of persons who have sought, in their interpretation of 

 Mr. Say's writings, a solution of problems of their own. For 

 integra we have very generally adopted the views of De Kay. 

 The species to which he evidently gives this name is clearly a 

 good species. Being subject to erosion, and seldom entirely free 

 from traces of it, Mr. Binney finds in that fact an evidence of 

 its identity with decisa. The same reasoning also probably in- 

 fluences him in a similar treatment of rufa, a species that is 



