234 A MANUAL OF AMERICAN LAND SHELLS. 



bifurcation or non-bifnrcation of the marginal teeth, the development 

 of the side cusps to the central and lateral teeth, and the presence or 

 absence of distinct cutting points to these cusps. I shall, however, 

 simply describe the dentition of our species, without reference to the 

 subgeneric or generic value of these differences of dentition or of the 

 peculiarities of the mantle, on which also generic and subgeneric dis- 

 tinctions have been founded. 



Species of Limax have been found in every quarter of the globe, but 

 they may be said to belong rather to the more temperate regions. In 

 North America they are less common in the tertiary portions of the 

 Southern States, but are found abundantly in the Middle and Northern 

 States and in the British possessions. Specimens were collected by 

 Mr. Kennicott as far north as the junction of the Yukon and Porcupine 

 Elvers, in Russian America. The Pacific States also are inhabited by 

 several species. I have received one from Lower California. The 

 genus is also found in the Central Province. The cellars and gardens 

 of the cities of the Atlantic seaboard are infested with several European 

 species, introduced by commerce. Like rats and mice and various de- 

 structive insects which have proceeded from continent to continent and 

 from island to island in the same manner, they occupy the houses and 

 other structures in the immediate vicinity of man, preying upon the 

 fruits of his industry and consuming his stores of provisions. Like 

 them, they thrive only in the vicinity of and, as it were, in contact with 

 man, and never withdraw from him to resume their original manner of 

 living in the wild-«!. These habits are the cause of much mischief, and, 

 when the animal are numerous, render them the pests of the house and 

 the garden. Their increase, therefore, beyond a certain point becomes 

 prejudicial, and means are adopted to keep them in check. In various 

 ways thousands of them are destroyed during the year, but their extra- 

 ordinary fertility enables them to make the loss good and to sustain 

 themselves in undiminished numbers. 



Species of the genus found in this country can be readily con- 

 founded only with those of the genus Avion, They can be at once dis- 

 tinguished by their smooth jaw, with its rostriform projection, that of 

 Avion being ribbed and regularly concave below; the respiratory orifice 

 of Limax is on the hinder part of the shield, while in Avion V is on the 

 anterior portion ; the rudimentary shell of Limax is strong, oblong or 

 square, while in Avion there are but irregular grains of calcareous mat- 

 ter. 



It will be noticed that the genitalia furnish reliable specific char- 



