204 



Fresh- Water Shells. 



Tlis shell has hitherto generally borne the name of P. trivolvis 

 in New England ; but it is not the trivolvis of Say, and is either 

 his P. lentus or a new species. 



PLA.NORBIS BiCAHINATUS. (Rackctt.) 



mx Shell orbicular, its tube rapidly increasing, 

 ■m deeply excavated on both sides, color brown- 



ish-yellow on the carina. Whorls rather more 

 than three, as seen on both sides, forming on 

 the nsht side a large and deep concavity, bounded by a sharp, 

 raised line or carina, and on the left side a still deeper, inversely 

 conic cavity, bounded by a similar carina, but of smaller circuit; 

 surface rather smooth, with faint, irregular lines of growth, most 

 distinct on the right side ; aperture ovate, right side broadest, and 

 on the general plane of that side of the shell ; left margin strongly 

 modified by the carina, and extending far beyond the plane of the 

 preceding whorl ; lip slightly expanded, white ; interior brownish, 

 with white lines in the grooves answering to the carina. Longest 

 diameter A inch, shortest diameter ^V inch. 



Animal light russet-color, beautituily dotted with amber ; foot 

 tongue-shaped, nearly as long as the diameter of the shell. The 

 strong angle of the aperture fully displays the respiratory opening, 

 which has a jagged flap, over which lies an acute groove ; move- 

 ments sluggish. 



Inhabits still w^aters, not so generally pools, as the margins of 

 large ponds. Not very common. 



This species is smaller than either of ths preceding, and is at 

 once distinguished from them by the very obvious angulairy of 

 the whorls on both sides, and by the very deep, conical cavity of 

 the left side. Sometimes a few faint revolving lines mny be found 

 on the surface. The tentacuia of the animal are usually very long 

 but sometimes one or both of them seem to have been broken. 



Planorbis Gampanulatus. — (Say.) 



Shell discoidal, yellowish or brownish-green, 

 lighter at the sides; diameter of its tube nearly 

 twice as great from side to side as in the contrary 

 dir>-ction ; right side exhibiting scarcely more 

 than two whorls, which are elevated to an obtuse rido-e, and form 

 an umbilical vortex very nearly perforating the shell ; on the right 



