31. Usually with a trace of an umbilicus, almost covered by the reflected lip; 



shell solid; lip joins body at an acute angle, making a loop-shaped or 

 shouldered aperture; from Alabama to Texas northward, in stagnant 

 pools 



Physa gyrina Say 

 No umbilicus; shell thin; body whorl rounded; N. Y. to Nebraska and 

 southward to the Ohio River; a lake species 



Physa sayii (Tappan) 



32. Aperture toothed or ridged; brackish water species 



Melampus lineatus Say Ear Shell 

 Aperture without teeth or ridges; fresh water species 33. 



33. Shell globular, usually about as wide as high; tentacles cylindrical; west- 



ern species 34. 



Shell higher than wide; tentacles flattened; generally distributed; Lyrri' 



naea (Fossaria) sp. — Common Pond Snails 35. 



34. With a deep umbilicus; shell often keeled around top of whorls 



Cannifex newherryi (Lea) Terraced Pond Snail 

 Scarcely or not perforated 



Parapholyx ejfusa (Lea) California Pond Snail 

 {Pompholyx effusa Lea) 



35. Body whorl large and inflated; aperture large and oval or rounded 36, 

 Body whorl compressed or narrow; aperture moderate to narrow 40. 



36. Spire long and slender, usually longer than the aperture 



Lymnaea (Lymnaea) stagnalis (Linn.) 

 Spire rather thick and usually equal to or shorter than the aperture 37. 



37. Spire much shorter than the aperture 38, 

 Spire only a little, if any, shorter than the aperture 39. 



38. Aperture much inflated, larger than the shell; a European species intro* 



duced into the eastern states 



Lymnaea (Radix) auricularia (Linn.) 

 Body whorl and aperture lengthened; native species 

 Lymnaea (Lymnaea) columella Say 

 (Pseudosuccinea columella (Say) ) 



39. Columellar area of aperture very broad; over 1" high 



Lymnaea (Bulimnea) megasoma Say 

 Columellar area of aperture narrower; smaller 

 Lymnaea (Stagnicola) emarginata Say 



40. Shell very long and narrow; upper whorls as high as, or higher than, 



wide 41. 



Shell narrow, but with the upper whorls wider than high 42» 



41. Aperture extremely narrow, with a continuous lip; shell unlined 



Lymnaea (Acella) haldemani Desh. 

 (Lymnaea gracilis Jay) 

 Aperture oval; lip not continuous; shell with growth lines 

 Lymnaea (Stagnicola) reflexa Say 



118 



