CONCHOLOGIA CESTRICA. 



47 



Shell obtuse-conic, reddish brown; s.\ 

 whorls 6, heavily ribbed, above, more 

 smooth beneath ; lip thickened, some- 

 what reflected; base flattened; umbilicus 

 small ; aperture narrow-lunate, with three 

 revolving lamina, on the parietal wall 

 one at the base ; and two, far within the 

 outer lip, near the base ; lingual mem- 

 brane with 78 rows of 13-1-13 teeth, 

 each ; buccal plate slightly arcuate, mi- 

 nutely notched on the cutting edge. H. 2%, W. 

 mill. 



Lingual Dentition of S. labyrinthica. [Morse.] 



Fig, 77, 



Station, under the bark of decayed logs. Chester 

 County; frequent. 



Sub-genus HELICODISCUS, MORSE, 1864. 



Animal of Helicodiscus lineata, enlarged. [Morse.] 



Fig, 78, 



Shell minute, flat ; whorls equally visible, above and 

 below, with revolving striae ; unicolored, whitish ; one, 

 or more, lamellar teeth, within the outer lip. 



