Aperture less than I/3 the length of the shell, body whorl smaller. 



C. exiguum (Say) Gld. 



26. — Pupoides marginaius (Say) Pils. & Van. 

 21.—Fupilla 



About 4 mm. long; aperture with 1 or 0 teeth on parietal wall. 



P. muscorum (L.) 



About 3 mm. long; parietal and columellar teeth each 1, and 1 

 tooth at base far within. Loess. P. Mandi Morse. 



About 2.5 mm. long; apex more conical; aperture with 4 teeth. 

 Loess. P. decora (Gld.) 



28. — Bifidaria 



Length 3 or more mm. ; short fusiform ; aperture constricted, peris- 

 tome expanded, teeth 4, prominent, almost closing aperture. 

 Length=3 mm. B. contracta (Say) Sterk. 



Length=4 mm. B. armifera (Say) Sterk. 



Length less than 3 mm.; aperture not constricted. 

 Length 2 to 2.5 mm. ; shell more or less cylindrical. 



Brown; cylindrical, narrow. B. procera (Gld.) Sterk. 



Whitish or horn colored. 



Parietal tooth 1, or 0; no other teeth. 



B. corticaria (Say) Sterk. 

 Teeth in aperture several. B. pentodon (Say) Sterk. 

 Length less than 2 mm. 



Cylindrical. B. holzingeri (Sterk.) 



Ovate, somoTvhat broader. B. curvidens (Gld.) Sterk. 



29. — Vertigo 



Length 2 or more mm. 



Length=2 — 2.5 mm.; diam.=l mm.; teeth 3. V. tridentata Wolf. 



Length=2 mm. ; diam.=l mm. ; teeth 5. V. gouldi (Binn.) Stimp. 



Length=3 mm., diameter=1.5 mm. V. ovata Say. 



Length less than 2 mm. 



Length about 1.6 mm. V. hollesiana (Morse) 



Length less than 1 mm. F. milium (Gld.) Binn. 



30. — Punctum pygmaeum (Drap.) Binn. 



31. — Oreohelix iowensis (Pils.) Loessi 



32. — Pyramidula. 



More than 10 mm. in diameter; spotted. P. alternata (Say) Pils. 

 Less than 10 mm. in diameter; color uniform. 



Eeddish brown; umbilicus very wide; diameter=8 mm. 



P. perspectiva (Say) Pils. 

 Dull brown or horn colored; umbilicus narrow; diameter 6 mm. 

 Both upper and lower surfaces of body whorl distinctly 

 ribbed or strongly striate. P. striatella (Anth.) 



Lower surface of body whorl smooth. 



(In Iowa a loess fossil only.) P. sMmeMi (Pils.) Shim. 



33. — Circinaria concava (Say) Pils. 



34. — Euconulus fulvus (Drap.) Eeinh. 



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