20— Physa 



Body whorl shouldered, spire rather abrupt. P. Integra Hald. 



Body whorl rounded, spire more regularly conical. 



Shell thin, inflated; whorls of spire rounded; aperture % the 

 length of the shell. P. sayi Tapp. 



Shell rather heavy; aperture less than ^ the length of the shell. 



P. gyrina Say. 



(Other forms, probably varieties of this species, occur in 

 the state.) 



21. — Segmentina 



Aperture white, strongly constricted; teeth 6. S. crassilahris Walk. 

 Aperture blackish, not constricted; teeth 5. 



S. armigera (Say) H. & A. Ad. 



22. — Planorhis 



Greater diameter more than 12 mm. 



Body whorl constricted behind the campanulate aperture; body 

 whorl narrow. P. campanulatus Say. 



Body whorl not constricted, aperture not campanulate; body 

 whorl gradually enlarging. 

 Sharply spirally carinate, often with second less prominent 

 carina; diameter 12 to 13 mm. P. hicarinatus Say. 



Not sharply carinate; diameter about 18 mm. 



Whorls spirally sculptured on the lower side, and within 

 the umbilicus. P. truncatus Miles. 



Whorls not spirally sculptured below. P. trivolvis Say. 

 Greater diameter less than 10 mm. 



Shell much flattened, with very sharp spiral carina. 



P. exacutus Say. 



Shell not sharply carinate. 



With revolving lines of hairs; pale. P. albus Muell. 



Without hairs; shell horn colored. 



Body whorl deflected downward, rounded; diameter 19 

 mm. P. defleetus Say. 



Body whorl scarcely deflected; diameter less than 10 mm. 

 Body whorl gradually enlarging, aperture not expanded. 

 Umbilicus deep, narrow; grayish white. 



P. umbilicatellus Ckll. 

 Umbilicus wide; shell horn colored. P. parvus Say. 

 Body whorl abruptly enlarged, aperture expanded. 



P. dilatatus Gld. 



23. — Cochlicopa liibrica (Muell.) Fer. 



24. — SpJiyradium edentulum (Drap.) Pils. 



(The elongated form with distorted body whorl which occurs in 

 the loess is knovrn as S. edentiduni var. alticola (Ing.) Pils.) 



25. — Carycliium 



Aperture more than ^ the length of the shell, body whorl relative- 

 ly large. C. exile H. C. Lea. 



83 



