297 



viously found abundant, are scarcely to be seen, even in the 

 most favorable localities this season, owing no doubt to the 

 same influences. 



It may be a subject wortTiy of consideration, to inquire whether 

 a similar mortality among the mollusca, in other regions, may 

 not have some connection with the peculiar oils observed in 

 bodies of water in various parts of the country during the last 

 j'ear; also, to ascertain whether an extensive mortality of this 

 kind would not naturally favor a large development of the 

 microscopic beings that have been studied with reference to this 

 matter. 



I hope soon to have the pleasure of laying before the Society 

 specimens of an undescribed species of Amnicola that is found 

 in the Mohawk River; also specimens of a minute species of 

 Limncea, which appears to have been erroneously referred to 

 L. caperata Say by De Kay. 



About four miles from Mohawk, N. Y., is a locality abounding 

 in calcareous tufa, in which, in some places where the formation 

 appears to have attained great age, shells of LiiimcEa eJodes Say, 

 are inclosed. 



The tufa in question exists in various parts of the State, and 

 in several localities in this county. F. E, Spinner, Esq., of this 

 place, who is conversant with the geology of this county, is of the 

 opinion, that the tufa is derived from water that has filtered through 

 rocks known as the " Water Lime Rocks of the New York 

 Geological Survey." This is inferred from the crumbly texture 

 of the rocks in the vicinity of localities where the tufa occurs, 

 and from the position of the tufa, — it being always just below 

 where the Water Lime Rock crops out, or in a position corre- 

 sponding thereto. 



There is a small triangular Cyclas found in the waters of this 

 latitude, extending from the Connecticut River, as far west as 

 Kalamazoo River, Michigan. The species in question varies with 

 the locality ; in some instances so much as to have been described 

 by different names. I am induced to regard it as C. edentula 

 Say. It may be embraced under the following synonymy : — 

 Cyclas edentula Say. 



" rliomhoidea Say, of Adams and Linsley. 



