134 THK NAUTILUS. 



It would be gratifying to know the results of these experiments. 

 Dr. Lewis' language implies that the species which he deposited in 

 Schuyler's Lake in 1868 did not inhabit the Susquehanna nor any 

 of its tributaries previous to that year. Perhaps some of the readers 

 of the Nautilus have specimens of some of these species taken from 

 the Susquehanna. If so they may be able to show that Dr. Lewis 

 was mistaken in supposing that the species did not inhabit the Sus- 

 quehanna; or that his experiments were successful. 



So far as Vivipara contectoides is concerned, his attempt to 

 colonize it in the Mohawk River and Erie Canal has been eminently 

 successful. The species is firmly established in both the canal and 

 river, and has spread many miles from the place of its introduction. 

 Beautiful specimens are abundant in tlie neighborhood of Albany, 

 occurring in the Erie and Cham2:)lain Canals and in the Mohaw^k and 

 Hudson Rivers. The specimens found here do not show any varia- 

 tion from specimens taken in the natui-al habitat of the species. 



Incidentally it may be remarked that Dr. Lewis' experiment 

 emphasizes the importance of carefully prepared local lists of 

 species ; and the importance of recording the dates on which spec- 

 imens are collected. There is no doubt that the geographical 

 distribution of many species of mollusca is being more or less 

 influenced by human agencies. This is especially true of fresh- 

 water species. Canals have been dug in various parts of the 

 country, connecting the waters of streams which difier widely in their 

 faunjB. Other canals are in the course of construction and many 

 others are projected. It is probable that some species of fresh-Avater 

 shells will thus be afforded the means of extending their habitats. 



In future years it will be desirable to know, for a given locality, 

 what species are indigenous and what sjjecies have been introduced. 

 In order to obtain this knowledge it is absolutely necessary that 

 there should be exhaustive lists or collections of the species of the 

 given locality made before the operation of man's disturbing 

 influences. 



ON AN UNDESCRIBED CYTHEREA FROM THE GULF OF MEXICO. 



BY W. H. DALL. 



Cytherea texasiana, n. s<. 



Shell resembling in general features C. convexa Say, but larger 

 more elongate in proportion and with a more delicately sculptured 



I 



