The Pond Snails 



Animal with short, ovate foot, short head and slender tentacles. 

 Sluggish snails, in stagnant or slow running water. Distribution 

 world-wide. 



The Three-coiled Orb Snail (P. trivolvis, Say) is found in 

 almost every pond, stream and ditch in this country, and should 

 be popularly known. Its rounded coils increase with age, so the 

 spire is at the bottom of a cup-like depression opposite the um- 

 bilical pit. Fine, close-set, knife-edged striations cross the 

 whorls. The lip is callused within. Diameter, i inch. 



Habitat. — Canada and United States. 



P. campanulatus, Say, has a bell-shaped aperture. Length, 

 i inch. 



Habitat. — New England to Minnesota. 



P. bicarinatus, Say, has two distinct keels and an enlarged 

 aperture with angled lip. Diameter, ^ inch. 



Habitat. — Canada to Kansas and Georgia. 



Shells of Planorbis are delicate and easily warped in growth, 

 so many monstrosities are found. Doubtless many named 

 varieties are erected upon abnormal individuals. 



THE SHIELD SNAILS. RIVER LIMPETS 

 Genus ANCYLUS, Geof. 



Shell patelliform, not spiral, thin; apex sinistral; jaws, 

 three; radula broad, crowded with teeth; foot large; mantle 

 included; tentacles triangular; pulmonary orifice protected by a 

 flap. 



A. rivularis, Say, has a horny, opaque shell, with blunt, 

 sub-central apex. The large, oval aperture narrows at one end. 

 Lining white. This is found adhering to stones in rivulets. 

 Length, i inch. 



Habitat. — Massachusetts, Virginia, Wisconsin. 



A. Newberryi, Lea, is a large blunt dome, smoky red, with 

 sides somewhat compressed, making an elliptical aperture. This 

 is easily the largest species in the genus. Length, i inch. 



Habitat.— Lake Klamath, Cal, 



295 



