414 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



E. ELASMOGNATHA. 



Jaw in a single piece, with an accessory, quadrate plate above. Marginal teeth 

 quadrate. 



SUCCINEA, Dr. 



Animal heliciform, thick and blunt before, short and pointed behind ; mantle 

 central, simple, protected by a shell which does not conceal the whole retracted 



animal; respiratory and anal orifices on the right of 

 Fig. 291. ^jjg mantle edge, under the peristome ; generative ori- 



fice behind the right eye-peduncle ; no caudal mucus 

 pore ; locomotive disk (?). 

 . . , ,„ Shell imperforate, thin, ovate or oblong; aperture 



Auimal of o. rustuana. * o » i 



large, obliquely oval ; columella simple, acute ; peri- 

 stome simple, straight. 



The frenus is world-wide in its distribution. 



The habits of the animal do not vary much fi-om those of Helix. They are 

 described in many works as being amphibious, which means that they possess 

 the power of living in the water as well as upon the land. Such appears to 

 have been the opinion of Lamarck. They are not, however, in any proper 

 sense amphibious, as they live upon the land exclusively, and breathe air; 

 and some of them occupy situations very distant from bodies of water. It is 

 not difficult, however, to account for this general belief. Some of the species 

 inhabit wet localities at the borders of swamps and ponds, and are even found 

 attached to the leaves of plants growing out of the water. They resemble also, 

 in external characters, certain species of Limnoea, which live in the water 

 itself. The two have, therefore, been confounded in popular belief. 



It is also stated very generally, that they cannot withdraw their bodies en- 

 tirely into their shells. This is certainly an error as regards the American 

 species, and probably as to all others. They all retire into their shells on the 

 approach of winter, and during seasons of drought; every part of the body is 

 then retracted within the plane of the aperture, and over it is extended a mem- 

 branous epiphragm, like that of our Helices. They cannot, however, retract 

 the body much beyond the plane of the mouth, and the foot is never wholly 

 drawn into the aperture of the mantle and concealed by it, as in Helix ; the 

 posterior extremity of the locomotive disk being always visible, on a level with 

 the mantle or collar. 



The e[)i|)hragm sometimes possesses considerable thickness and consistence. 



Jaw with an upper, quadrangular, accessory plate. The jaw is strongly 

 arched, the ends acuminated in aS. avara (Fig. 293), blunt in obliqua, ovalis, 

 Totteniana (Fig. 202), campesh-is, lineata, and effusa ; there is a median pro- 

 jection to the cutting margin, sometimes broken by the ends of ribs. These 

 ribs are found in S. Totteniana (3) (see Fig. 292); S. obliqua (3-7); ovalis 

 (over 7) ; I detected no ribs on that of S. avara, lineata, campestris, Nuttalli- 

 ana, Sillimani, Haydeni, or effusa. 



