MOLLUSCS. 



313 



appear probable that it came along with hot-house plants, or that its eggs may have 

 adhered to some wine cask and found suitable conditions for development in the 

 cellars of the new world. Many other species are found in the United States, most of 

 them being small and inconspicuous, Z. milium being one of our smallest shells. 



The genus IlelLv has been divided into innumerable sub-genera and tribes, the de- 

 tails of which should lie sought in special works. This genus is the first of the sub- 

 familv Ilclicina^, in which the spiral shell is thicker and stouter than in the preceding 

 divisions, and capable of containing the entire animal when retracted. Most of the 

 species have the outer lip thickened and reflected, and not infrequently the aperture is 

 greatly reduced by tooth-like processes which 

 may arise fi'om the columella or the outer lip, 

 or from both. The species are usually much 

 larger than those in the sub-families just passed. 



The characters of the genus Helix are very 

 poorly defined, and the shape of the shell varies 

 between very wide extremes. In some the 

 spiral is high, in others it is nearly flat. In 

 most of our northern species the shell is horn- 

 colored without ornamentation, but in the 

 tropics brightly colored species are the rule. fig. siw. — y/i/i,c iH./.(»r«,MB. 



The color may be laid on in blotches, or more 



frequently in stripes, which follow' the spiral of the shell as in the adjacent figure of 

 Ilc'/i.r siidunensis, which, as its name indicates, comes from Africa. 



With such a wealth of species to choose from (about thirty-five hundred being- 

 known) it is a difticult task to select the few which our space will admit. Our most 

 common s|>ecies is possilily HelLr <(lholabrls, which, when adult, reaches a diameter of 

 about one inch. In the young the outer lip is thin and sharp; but 

 when the full size has been reached, the lip becomes thickened and 

 reflected, or turned outwards, and covered with a white jiorcellanous 

 de])osit which gives the specific name. Usually the columella is 

 smooth, but occasionally specimens are found in which a tooth is 

 developed. This species is found most abundantly in forests of hard 

 wood. In the southern states its place is taken bv a similar but much larger S23ecies, 

 Helix major. 



The garden-snail of Europe, H. hortensis, has been introduced into several places 

 along our eastern coasts. It is very common on the islands in and near the harbor of 

 Salem, Mass., where, together with Helix alternata, it lives in the long grass and among 

 the juniper-trees. This species has a white lip, and is usually ornamented with a vary- 

 ing number of reddish lines which follow^ the spiral of the shell. Each 

 of the islands mentioned has its own peculiar pattern of ornamenta- 

 tion, which seems to have been derived from the first animals intro- 

 duced. The method in which this species obtained a foothold on 

 these islands (several of which are small and uninhabited, and sepa- 

 rated by a mile or more of salt water from the shore) is even less 

 easily decided than in the case of the Zoiiites cellaria. 



Sever.al of the European species are used as food, and one, Helix j^'imatia, the Koman 

 snail, has long occupied a place in the economy of the Latin races. This and Helix as- 

 persa are to-day extensively eaten by the French, and the latter species was introduced 



Fig. 361.— hmx 



bolabris, young. 



Fig. 36M. — HcU.t 

 ftortensLf, gar- 

 den snail. 



