67 



than the spire ; labium, calcareous deposit copious, not perfectly 

 appressed at base, but leaving a very small umbilical aperture. 

 Inhabits Cayuga Lake. Length 7-10 of an inch.* 

 Found by Mr. Augustus Jcssup. It is closely allied to L. ehdes, 

 but the whirls are more convex, one less in number, and the two 

 terminal ones are proportionally smaller ; the callus of the labium, 

 also, near its inferior termination, is applied still more closely to 

 the surface of the body whirl. 



Lymneus macrostomus. — Shell suboval; whirls five, body 

 whirl somewhat reticulated ; suture not profoundly indented ; spire 

 about two-thirds of the length of the aperture, acute ; aperture 

 much dilated ; labrum not thickened on the inner sub-margin. 



Inhabits Cayuga Lake. Length one half of an inch, and up- 

 wards. 



Imperfect specimens of this shell were found on the shore of 

 (Cayuga Lake, by Mr. A. Jessup, but they are sufficiently entire, 

 to exhibit considerable similarity to some varieties of L. auricn- 

 larius of Europe. It may readily be distinguished from L. catas- 

 copium, by its much more dilated aperture. 



Lymneus emarginatus. — Shell rather thin, translucent ; volu- 

 tions four, very convex; body whirl large; suture deeply im- 

 pressed ; spire somewhat eroded ; mouth two-thirds of the length 

 of the shell. 



Length nearly 4-5 of an inch ; of the mouth, half inch. 



Inhabits Lakes of Maine. This species was discovered by Mr- 

 Aaron Stone. 



It is a rather larger and considerably wider shell than L. catas- 

 copiuni, and the emargination visible on a profile view of the 

 umbilical groove is far more profound. 



Physa GYRiNA. — Shell heterostrophe, oblong; whirls five or 

 six, gradually acuminating to an acute apex; suture slightly im- 

 pressed ; aperture more than one half, but less than two-thirds of 

 the length of the shell ; labrum a little thickened on the inner 

 margin. 



Length rather less than one inch. 



Inhabits waters of the Missouri. 



[* The text gives 7-20ths, which is corrected by Mr. Say in the remarks 

 on L. humilis. — Ed.] 



