6 LAND AND FRESH-WATER SHELLS OF N. A. [PART L 



Spallanzani calls the tongue, is brought up against it, cutting 

 out and carrying into the mouth semicircular portions of nutri- 

 ment. This operation is carried on with great rapidity, and the 

 substance to be eaten soon disappears. It is certain, however, 

 that some species^ are also fond of animal food, and sometimes 

 prey upon earth-worms, their own eggs, and even upon each 

 other; but the slowness of their motions and their consequent 

 inability to pursue prey forbids the idea of their being dependent 

 on animal food. They, in their turn, become the prey of various 

 b4rds and reptiles ; and it is no uncommon thing to observe, in 

 the forest, clusters of broken shells lying dh logs or stones which 

 have been chosen by birds as convenient places for breaking the 

 shell and extracting the animal. 



The snails of the United States are for the most part solitary 

 in their habits, differing very much, in this respect, from the 

 snails of Europe. It is true that in localities favorable for their 

 residence they may be collected in considerable numbers ; and 

 especially is this the case in the States north of the Ohio River. 

 But even there, they seem to live independently of each other, 

 and not to unite into herds or communities. There are occasional 

 exceptions, however, as in the case of Helta; alternata, very large 

 numbers of which have been observed collected into a small space, 

 especially in winter, as if for the purpose of imparting warmth to 

 each other. The few species of European snails which have 

 been introduced retain their native habits. Helix horfensis, for 

 instance, which has been transplanted to some of the small islands 

 in the vicinity of Cape Ann, is found there in countless numbers, 

 literally covering the soil and shrubs. It is worthy of notice also, 

 that each island is inhabited by a variety peculiar to itself, showing 

 that the variety which happened to be introduced there has propa- 

 gated itself, without a tendency to run into other variations. 

 Thus, on one islet we have the yellowish-green, unicolored 

 variety, once described as Helix subglobosa; and on another, 

 within a very short distance, we find a banded variety, and none 

 others. 



In regard to colors, our snails are quite plain and exceedingly 

 uniform ; in this respect, also, differing essentially from the species 

 of the old world. They vary from yellowish-green through horn- 



' These are characterized by the lingual dentition : see Vermivora. 



