296 



After having collected large numbers of specimens from 

 various localities, I am induced to modify a formerly expressed 

 opinion, based somewhat hastily on conclusions drawn from hav- 

 ing observed reversed specimens among the embryonic young of 

 the shells of this region, namely, — that the reversion of the 

 specimens is a specific feature, I find it extends to the following 

 species : — 



P. Integra Say. most conspicuously. 



P. decisa " next. . 



P. ritfa Haldeman. 



P. ponderosa Say. 



P. ? an abundant shell of Mohawk River, very 



nearly related to decisa, but differing in some constant par- 

 ticulars.* 



Of the five species above named, I have reversed specimens. 

 My efforts have been directed to procure, by exchange, large 

 numbers of Paludina in alcohol, for the purpose of ascertaining 

 what other species present this feature, and when I have further 

 facts to communicate in reference to it, I will lay them before 

 the Society. 



I have ascertained that that singular little shell, known as 

 LimncBa gracilis Jay, is to be found in the southern part of 

 Herkimer County, N. Y., (Little Lakes,) and in the northern 

 part of Otsego County, (Schuyler's Lake.) Thus far, I have 

 found only a single fragment in the first-named locality, and a 

 few eroded abandoned shells in the latter. 



The extreme drought of previous seasons has had the effect, in 

 some of the smaller bodies of water I have examined this season, 

 to destroy great numbers of the bivalve molluscs that inhabit 

 them ; and, in some localities, the Anodonta fliiviatilis Lea, is 

 almost exterminated. Many other molluscs that I have pre- 



* 1st. The plane of the aperture forms a larger angle with the axis of the 

 shell, than in decisa. 



2d. The labrum is usually formed by the margin of the shell continuing 

 around the aperture in the same plane, while in decisa the margin is a little ex- 

 cavated just at or above the extreme periphery of the last whorl. 



3d. The shells of the Mohawk River are less liable to erosions than P. integra, 

 which is sparingly associated with them ; while decisa is always more eroded 

 than intcf/ra, when they are found together. 



