GASTROPODA 



517 



4 to 7 teeth; anterior tentacles absent: a circumboreal genus, with 

 about 36 American species. 



Key to the species of Vertigo here described: 



Oj But 1 parietal tooth V. VENTBICOSA 



a a Two parietal teeth. 



Z>! Shell over 2 rnm. long V. OVATA 



6 a Shell about 1 mm. long V. MILIUM 



V. ovata Say (Fig. 792). Shell ovate, dark amber-colored, smooth, 

 and shiny; outer lip of aperture indented; 6 to 12 teeth, 2 or 3 parietal, 

 2 columellar, and 2 to 6 on the lip; length 2.2 mm.; diameter 1.5 mm.: 

 North America; the commonest species. 



V. ventricosa (Morse). Shell ovate, smooth, and polished, with 4 

 whorls; lip of aperture with a deep indentation; teeth 5, 1 parietal, 2 



Fig. 791 



Fig. 792 



Fig. 793 



Fig. 791 Bifldaria armifera (Binney). Fig. 792 Vertigo orata (Morse). 

 Fig. 793 Vertigo milium (Morse). 



columellar, and 2 on the lip; length 1.7 mm.; diameter 1.1 mm.: north- 

 eastern and north-central America; California. 



V. milium (Gould) (Fig. 793). Shell ovate and very minute; dark 

 amber in color; lip of aperture indented; teeth 6 to 8, 2 parietal, 2 

 columellar, 2 on lip, the upper one being large and sharply bent down- 

 wards at its inner end ; length 1.4 mm. ; diameter 

 .8 mm. : America, east of the Mississippi River 



5. STROBILOPS Pilsbry. Shell more or less 

 helicif orm with 5 or 6 striated whorls ; parietal 

 wall with several entering revolving lamellae: 

 5 American species. 



S. labyrinthica (Say) (Fig. 794). Shell with 6 whorls, 2.1 mm. 

 wide and 1.6 mm. high, with 3 parietal lamellae, each of which has 

 swellings at regular intervals: eastern and central states. 



Fig. 704 StrnWlops laby- 

 rinth ica ( Walker) . 



FAMILY 3. COCHLICOPIDAE. 



Shell elongate, slender, conical, without umbilicus; aperture eden- 

 tate, rounded, or lengthened; ureter straight: 200 species, cosmopolitan. 



COCHLICOPA Ferussac. Shell smooth and glossy; jaw slightly 

 arched, without ribs and with a median projection : 2 American species. 



