516 MOLLUSCA 



tentacles long; anterior tentacles very short: cosmopolitan; numerous 

 species, 6 American, mostly in the West. 



P. muscorum (L.) (Fig. 788). Shell stout, cylindrical, with 6 or 7 

 whorls; aperture nearly circular, either without or with 1 or 2 teeth; 

 length 4 mm. ; breadth 1.5 mm. : North America ; circumpolar. 



2. PTTPOIDES Pfeiffer. Shell rather slender and tapering, with 6 or 

 7 whorls, smooth and shining; aperture ovate, without teeth: in all 

 continents except Europe; 3 American species. 



P. marginatus (Say) (P. fallax Say) (Fig. 789). Jaw strongly 

 arched; umbilicus deep; length 5 mm.; diameter 2 mm.: United States, 

 east of the Rocky Mountains. 



3. BIFID ART A Sterki. Shell conical or ovate, smooth or finely 

 striate; aperture dentate with usually a large bifid parietal lamella, 2 

 lipfolds, and a basal tooth; additional teeth sometimes present: about 

 22 American species. 



Key to the species of Bifidaria here described: 



! Aperture almost edentate B. CORTICARIA 



o a Aperture with prominent teeth. 



6 Aperture nearly closed by 4 or 5 large teeth B. ARMIFERA 



Z> 3 Aperture with 5 to 9 smaller teeth B. PENTODON 



Fig. 788 Fig. 789 Fig. 790 



iscorum (Morse). Fig. 789 Pupoides 

 Fig. 790 Bifidaria corticaria (Binney). 



Fig. 788 Pupilla muscorum (Morse). Fig. 789 Pupoides marginatus (Binney). 



' (Binn 



B. corticaria (Say) (Fig. 790). Shell white, shining, cylindrical, 

 with an obtuse apex; whorls 5 to 6, convex; aperture with but 1 or 2 

 teeth on parietal wall, or none, and a very blunt tooth on the columellar 

 wall; length 2.5 mm.; diameter 1 mm.: eastern states, to the Mississippi. 



B. armifera (Say) (Fig. 791). Shell cylindrical, with 6 to 7 whorls; 

 aperture with a wide rim and 4 to 6 teeth, the parietal lamellae large, 

 irregular, with 1 or 2 projecting points; columellar lamella thick and 

 situated deep in the aperture; lipfolds 2; length 4.5 mm.; diameter 2.2 

 mm. : from the Atlantic to the Rocky Mountains. 



B. pentodon (Say). Shell conical, white, whorls 5, convex; aper- 

 ture with a broad rim and with 8 teeth, the parietal and inferior lip 

 lamella curved to the left; length 2 mm.; diameter 1 mm.: America. 



4. VERTIGO Draparnaud. Shell ovate or conical, with 4 to 6 convex 

 whorls; apex obtuse; aperture with a narrow, white rim, the outer lip 

 of which is usually straightened or indented at its upper third; with 



