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 crescentic, with a median projection: 2 American species. 



H. parallelus (Say) (H. lineatus 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. PUNCTUM Morse. Shell depressed and discoidal, small or minute ; 

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

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



P. pygmaeum (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 ribs; 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 pygmceum (Binney). 

 Fig. 810 Bulimulus dealbatus (Binney). 



BTTLIMULUS 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. CIECINABIIDAE. 



Shell either internal or external and heliciform, thin, 

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

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

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

 like teeth, the animals being carnivorous; ureter reflexed: 

 12 American species, all on Pacific slope but one. 



CIRCINARIA Beck. Shell external: several species. 



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

 color whitish: eastern and central states. 



