﻿50 
  PKOCEEDINGS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  or 
  dark 
  inside 
  ; 
  outer 
  lip 
  tliia 
  and 
  acute, 
  slightly 
  sinuous, 
  advancing 
  

   slightly 
  below, 
  retracting 
  a 
  little 
  towards 
  the 
  columella 
  and 
  above. 
  

   Columella 
  concave, 
  broadly 
  white-calloused. 
  Parietal 
  wall 
  in 
  adults 
  

   covered 
  with 
  a 
  rather 
  thick 
  white 
  callus, 
  heavier 
  towards 
  the 
  posterior 
  

   or 
  upper 
  angle. 
  

  

  Fig. 
  4. 
  Lithasiopsis 
  Mexicanus, 
  u.sp. 
  

  

  Length 
  16 
  ; 
  diam. 
  8'2 
  mm. 
  ; 
  aperture 
  7'8 
  mm. 
  long. 
  

   ,, 
  17-5 
  ,, 
  8 
  ,, 
  ,,7 
  ,, 
  ,, 
  

  

  .) 
  15 
  ,, 
  7-3 
  ,, 
  ,, 
  6-8 
  ,, 
  ,, 
  

  

  Operculum 
  like 
  that 
  of 
  L. 
  Hinkleyi. 
  

  

  Hah. 
  — 
  Montezuma 
  River, 
  at 
  the 
  ford, 
  a 
  short 
  distance 
  above 
  Tampa- 
  

   molon. 
  State 
  of 
  San 
  Luis 
  Potosi, 
  Mexico. 
  

  

  This 
  species 
  has 
  the 
  appearance 
  of 
  a 
  Goniolasis, 
  but 
  differs 
  from 
  

   that 
  genus 
  by 
  its 
  calloused 
  columella. 
  The 
  dominant 
  colour 
  form 
  

   is 
  dull 
  yellow, 
  with 
  one 
  or 
  several 
  dusky 
  bands 
  on 
  the 
  last 
  whorl 
  

   and 
  a 
  bicoloured 
  spire, 
  each 
  whorl 
  light 
  above, 
  dark 
  below; 
  but 
  

   some 
  examples 
  are 
  uniform 
  yellowish 
  or 
  yellowish 
  brown, 
  and 
  very 
  

   few 
  (4 
  per 
  cent, 
  in 
  the 
  lot 
  examined) 
  are 
  purplish 
  or 
  brownish 
  

   black. 
  

  

  