OF CONCHOLOGY. 243 



from which direction it may have been introduced. Cfon. vir- 

 ginica also may be included under the same remarks. Soma- 

 togyrus isogonus very probably came from the west, as well 

 also Amnicola tustrica. The species of Vitrina may possibly be an 

 established species — manifesting its presence periodically here, 

 as it has been observed to do in the vicinity of Portland, Maine ; 

 or it may have been introduced from Canada on the rafts of 

 lumber that are floated down the Erie Canal. 



So far as at present observed, the species enumerated above 

 are all that appear to have been introduced in the territory under 

 consideration since 1853. While these additions to a local fauna 

 have been in progress it has been ascertained that among the 

 terrestrial molluscs many of the larger species have become quite 

 scarce. There are two conspicuous reasons for their decadence. 

 Primarily, the progressive clearing of forests destroys their 

 abodes. Secondly, the greater exposure incident to the destruc- 

 tion of the forests enables birds and field mice to exert their 

 carnivorous instincts on the snail with more certainty. 



In speaking of the depredations of field mice on the larger 

 snails, it may be remarked that this class of mammals has mul- 

 tiplied excessively — no doubt in consequence of the destruction 

 of the harmless snakes which otherwise would abound in 

 sufficient numbers to keep this class of animals within due 

 bounds. 



Many of the smaller species of terrestrial molluscs, especially 

 such as delight to haunt the margins of water, and are too small 

 to engage the carnivorous instincts' of the field mice, continue to 

 occupy available stations in undiminished numbers. 



In a territory thatyields scarcely more than a hundred species of 

 mollusca to the collector, it would not seem probable that any con- 

 siderable number of these species would present features which 

 would render them interesting on account of peculiarities not 

 exhibited by the same species in other regions. This indeed is 

 true to such an extent that scarcely half a dozen species may be 

 mentioned as exhibiting local peculiarities worthy of especial 

 mention. Mention has frequently been made of some of the 

 peculiarities exhibited by Melantho Integra in the Erie Canal at 

 Mohawk. Briefly it may be repeated here that abnormal varie- 

 ties and. reversed specimens are a conspicuous and not a very 

 uncommon feature, and that these peculiarities of development 

 are exhibited in greatest profusion in a portion of the canal re- 

 markable for its great width and depth. In the Mohawk river 

 are found two species of Melania in remarkable abundance. 

 One of these (Trypanostoma subulare, Lea,) attains large size 

 and is found in immense numbers in sluggish water, where the bed 



