MOLLUSCS. 



317 



seven liuu<lreil nnmiiKiI speeies being (Usti-il)uted in Europe, Asia, and Afriea. The 

 shell is long and cylindrical or fusiform, and is usually coiled from right to left, although 

 dextral forms occur. The animal is also sinistral, the genital and respira- 

 tory orifices being on the left side of tiie body. The aperture is usually 

 distinct from the rest of the shell, being separated by a neck or constric- 

 tion. We liave already alluded to the peculiar jiernianent epiphragni 

 'vitli which these forms close the aperture. 



The members of the family Succinid.e have a world-wide distril)u- 

 tiiin, and are usually found near the nnirgins of ponds and streams. The 

 shell much resembles that of the Limne.ins, though tlie two families are 

 widely different. The family is distinguished from all others by the 

 upper jaw, which consists of the usual arcuate portion backed up by a 

 quadrate plate. The shell is very thin and transi)arent, .ind niudc u]i of 

 a few rapidly enlaroing whorls. The principal genus is ,Succineu, of fi«-. SbS. - c/om- 

 which about two hundred s]iecies are known. These forms have an 



oval aperture and a sharp outer lip, and are usually 

 ' c regarded as amphibious or even as preferring a sub- 



m/%, i^v aquatic life. This belief does not appear to be well 



V J \ 1 founded, for, although they are found near the mar- 



gins of streams, thi'V li\i' exclusively in the air, 

 Fic,.3S9. — a, Succineatotteniana: b, fi. and some of tlu'ui are found far from any body of 



oralis ; c, S. avara. ■' ■' 



water. 



At the time of drought, and nt the npproai'Ii of winter, they draw the body com- 

 pletely within the shell, .'uid form an epijihragni like that of the Hdkes. The shell 

 is amber-colored or whitish. Our most common species are SucrAnea avara, and S. 

 obliqiia. 



The terrestrial ])ulmonates in which the shell is internal or absent are known in 

 popular )iarlanee as slugs, while in scientific works they are united into a family to 

 which the name LijrAciDJS is applied. Their general a))]>earance is too well known to 



call for any detailed descrijitiou, yet there are certain features which have a morpho- 

 logical significance to be mentioned. On the dorsal surface of the body, near the 

 anterior end, is a fleshy plate, the mantle. At or near the i-ight margin of this, 

 is the opening of the respiratory pore. The iiead is well defined and provided with 

 tentacles. 



The slugs are chiefly nocturnal, and this fact accounts for the few ordinarily seen, 

 although there may be thousands about. In the daytime they secrete themselves 

 under boards, fallen trees, etc., where there is at least partial darkness, but at night 

 they come out to feed. They do a great amount of diunage in gardens, as they feed 



