150 Illinois State Laboratory of Natural History. 



Family LiMNiEiD^. (Pond Snails.) 



Physa ancillaria^ Say. 



(Say, Jour. Acad. Nat. Sci. Phil., v, 124, 1825.) 

 Common in Long Lake and in Willow Slough. The larg- 

 est examples taken measure about .50 inch in length. 



Physa heterostropha, Say. 



{Lininea heterostropJia, Say, Am, ed. Nich. Enc, pi. i, fig, 

 6, 1817, 1818, 1819 [as cited by Binney].) 



This was probably the most common snail in the bottom- 

 land pools. It is one of the thin-shelled species, with about 

 four whorls, and differs from the preceding in having a longer 

 and more tapering spire and a narrower aperture. Otherwise 

 they are much alike. This is one of the most active and wide- 

 ly distributed of the species taken. It is said sometimes to 

 attack and devour insects as large as itself. The eggs are 

 deposited, according to Say, in the month of May, but proba- 

 bly at intervals during the summer also. Egg masses, which 

 in all probability were from this snail, were quite frequently 

 found attached to the outside of shells, where they had been 

 left by other individuals. The shells were frequently clothed 

 with growths of stalked iufusorians. 



Localities: Harkness Slough, Quincy Bay, Willow Slough, 

 Cedar Creek, Wood Slough. 



Helisoma trivolvis, Say, 



(Planorhis trivolvis^ Say, Am. ed. Nich. Enc, pi. ii, fig. 2, 

 1817, 1818, 1819.) 



Common in many of the pools. Easily recognized by its 

 depressed shell, — the whorls lying nearly in one plane so that 

 they can be followed on two sides of the shell. Large examples 

 taken, measure five eighths of an inch in diameter. 



Localities: Harkness Slough, Willow Slough, Lily Lake, 

 Long Lake, Wood Slough. 



Family VALVAXiD.Ti. 



Valvata tricarinata, Say. 



(Cyclostoma tricarinata, Say, Jonr. Acad. Nat, Sci. Phil., i, 

 13, 1818.) 



