22 Bryant Wai,ke;r 



Subfamily NEOPLANORBIN^ Hannibal, 1912. 

 Shell small, planorbiform or neritiform. 



Key to the genera of Neoplanorhince. 



Shell planorbiform Neoplanorbis. 



Shell neritiform Amphigyra. 



Genus NEOPLANORBIS Pilsbry, 1906. 



Shell very minute, planorboid, dextral, subdiscoidal, 

 nearly flat above, convex below, usually carinate at the 

 periphery; whorls two, rapidly enlarging; aperture very 

 oblique, wider than high, a little dilated at the base ; lip 

 thin, not continuous; columellar margin straight and 

 broadly dilated, somewhat thickened within. Dentition and anatomy so far 

 as known similar to AmpJiigyra. 



Type: N. tantUliis Pils., fig. 67. 



Fig. 67 



Genus AMPJ-ilGYRA Pilsbry, 1906. 



Shell minute, dextral, neritoid or 

 crepiduliform, imperforate, with a small, 

 depressed, lateral spire ; whorls about 

 ij^, very rapidly enlarging, the last very 

 convex dorsally ; apex smooth ; body- 

 whorl spirally striate ; aperture very 

 large, transversely oval ; lip continuous and full, thin ; cavity of the spire 

 very small, a thin, broad, concave, columellar plate projecting across the end 

 next the spire. 



Fig. 69 



Animal sinistral, externally lymnseid; tentacles short, blunt, cylindric; 

 eyes near their inner bases ; a short, false gill in the pallial cavity. Radula ar- 

 ranged as in Lymncsa, central tooth unicuspid, laterals bicuspid, marginals 

 low, wide, with four or five cusps. 



Type: A. alabamensis Pils., fig. 



Radula, fig. 69. 



