32 LIMACIDJE. 



mediately adjacent to, but a little above and anterior to 

 the respiratory orifice, with a cleft or fissure through the 

 mantle from the orifice to its edge. Orifice of organs of 

 generation near, and immediately behind, the superior 

 tentacle. Testaceous rudiment, thin, concentrical, not 

 spiral, covered above with a thin and transparent perios- 

 traca, below smooth. 



GEOGRAPHICAL DISTRIBUTION. Inhabits all parts of 

 the United States except, perhaps, the tertiary section 

 of the Gulf of Mexico, in which it has not yet been 

 noticed. There is every reason to believe that some of 

 the species will be found in that section also, although 

 not so numerously as in the more temperate climate 

 further north. The favorite locality of the genus is in 

 the milder parts of the temperate zone, where it flour- 

 ishes in great numbers. Individuals become less numer- 

 ous on approaching the equator, and also in going to 

 the extreme north. One or more undescribed species 

 are known to occupy the western coast of North Amer- 

 ica, in the Oregon territory. 



REMARKS. The animals of this genus appear to possess 

 the power of accustoming themselves to changes of cli- 

 mate and condition in a greater degree than any others 

 of the order ; hence they accompany man in his voyages, 

 and are found wherever he makes a permanent settle- 

 ment. Some of the European species are probably 

 found in every country, and almost upon every island 

 which has been colonized by Europeans ; and in the mari- 



