GASTROPODA 523 



2. Helicodiscus Morse. Shell disc-shaped, with the spire flat, and 

 the umbilicus broad and shallow, the last whorl with 1 or more internal 

 teeth ; jaw crescentie, with a median projection : 2 American species. 



H. parallelus (Say) (7/. Uncatus Say) (Fig. 808). Height 1.5 mm.; 

 diameter 4 mm., with parallel, raised, revolving- lines: eastern United 

 States, living under leaves, loose bark, etc. 



3. Ptjnctum Morse. Shell depressed and discoidal, small or minute ; 

 aperature large, with a thin lip and without teeth; jaw composed of 

 10 to 19 separate quadrate plates: circumpolar; 6 American species. 



P. pygmseum (Draparnaud) (Fig. 809). Umbilicus open; shell 

 minute; height 1 mm.; diameter 1.5 mm.: eastern United States. 



Family 8. BULIMULIDAE. 



Shell elongate, with a high conical spire; aperture elongate, eden- 

 tate; jaw arched with prominent libs; radula with central tricuspid 

 and lateral bicuspid teeth ; ureter reflexed : over 1,000 species, principally 

 in tropical America. 



Fig. 808 Fig. 809 Fig. 810 



Fig. 808 — Helicodiscus parallelus (Binney). Fig. 809 — Punctum pygmwum (Binney). 

 Fig. 810 — BuUmulus dealbatus (Binney). 



BuLiMULUS Leach. With the characters of the family: about 6 

 species in the United States, all southern. 



B. dealbatus (Say) (Fig; 810). Shell thin, white, with gray longi- 

 tudinal lines, 6 or 7 whorls; aperture oval, with an acute lip; 18 mm. 

 long; 12 mm. thick: southern states, north to North Carolina and Mis- 

 souri; common. 



Family 9. CIRCINAEIIDAE. 



Shell either internal or external and heliciform, thin, 

 with a wide umbilicus, depressed, with 5 whorls; aperture 

 large, with a somewhat thickened lip ; jaw crescentie, stri- 

 ated, with a median projection; radula with long thorn- ^^^ 

 like teeth, the animals being carnivorous; ureter reflexed: ^concavii' 

 12 American species, all on Pacific slope but one. (Baker). 



CiRCiNARiA Beck, Shell external: several species. 



C. concava (Say) (Fig. 811). Height 8 mm.; diameter 17 mm. 

 color whitish : eastern and central states. 



