MOLLUSCS. 



317 



Ctavr- 

 silia trmicata. 



seven hundred nominal species being distributed in Euroj)e, Asia, and Africa. The 

 shell is long and cyliudrical 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 the body. The aperture is usually 

 distinct from the rest of the shell, being separated by a necli or consti'ic- 

 tion. We have already alluded to the peculiar permanent ejjiphragm 

 with which these forms close the aperture. 



The members of tlie family Succinid^ have a world-wide distribu- 

 tion, and are usually found near the margins of ponds and streams. The 

 shell much resembles that of the Limneans, though the 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 transparent, and made up of 

 a few rapidly enlarging whorls. The principal genus is Succmea, of ^fi^^f^ 

 which about two hundred species are known. These forms have an 



oval aperture and a sharp outer lip, and are usually 

 regarded as amphibious or even as preferring a sub- 

 aquatic life. This belief does not appear to be well 

 founded, for, although they are found near the mar- 

 gins of streams, they live exclusively in the air, 

 and some of them are found far from any body of 

 water. 



At the time of drought, and at the approach of winter, they draw the body com- 

 pletely within the shell, and form an epiphragm like that of the Helices. The shell 

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

 obliqiia. 



The terrestrial pulmonates in which the shell is internal or absent are known in 

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

 which the name Limacid^ is applied. Their general appearance is too well known to 



Fig. 389. — a, Succinea totteniana ; b, S. 

 ovalis ; c, S. avara. 



Fig. 390. — Umax maxUnus. 



call for any detailed description, 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 right margin of this, 

 is the opening of the respiratory pore. The head 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 damage in gardens, as they feed 



