﻿47 
  

  

  A 
  NEW 
  MEXICAN 
  GENUS 
  OF 
  PLEUROCERATIDJ]]. 
  

   By 
  Professor 
  Henex 
  A. 
  Pilsbky. 
  

  

  Read 
  10th 
  December, 
  1909. 
  j 
  

  

  Among 
  tlie 
  shells 
  collected 
  by 
  Mr. 
  A. 
  A. 
  Hinkley 
  durmg 
  his 
  last 
  

   journey 
  to 
  Mexico 
  (January 
  and 
  February, 
  1909), 
  were 
  two 
  species 
  

   of 
  the 
  family 
  Pleuroceratidse 
  which 
  cannot 
  be 
  referred 
  to 
  any 
  of 
  the 
  

   known 
  genera. 
  Up 
  to 
  this 
  time 
  no 
  member 
  of 
  this 
  family 
  has 
  been 
  

   recorded 
  south-west 
  of 
  central 
  Texas, 
  where 
  Goniohasis 
  convalensis, 
  

   Pilsbry, 
  is 
  found 
  in 
  the 
  streams 
  of 
  Hays, 
  Cornal, 
  and 
  Bexar 
  counties.^ 
  

  

  LiTHAsioPSis, 
  n.gen. 
  

   Shell 
  varying 
  from 
  cylindric 
  with 
  conic 
  spire 
  to 
  ovate-turrite, 
  

   similar 
  in 
  contour 
  to 
  Goniohasis 
  or 
  Lithasia, 
  solid. 
  Aperture 
  ovate 
  

   or 
  piriform, 
  rounded 
  at 
  the 
  base 
  ; 
  outer 
  lip 
  thin 
  and 
  acute 
  ; 
  columella 
  

   concave, 
  broad 
  ; 
  parietal 
  wall 
  covered 
  with 
  a 
  heavy 
  callus, 
  which 
  

   is 
  thickest 
  near 
  the 
  posterior 
  angle 
  of 
  the 
  aperture. 
  Operculum 
  

   very 
  shortly 
  ovate, 
  nearly 
  circular, 
  the 
  nucleus 
  at 
  its 
  lower 
  fourth. 
  

   Inside 
  there 
  is 
  an 
  oblong 
  dull 
  area 
  of 
  attachment 
  along 
  the 
  columellar 
  

   side, 
  bounded 
  by 
  a 
  raised 
  border 
  or 
  brown 
  cord 
  ; 
  the 
  rest 
  of 
  the 
  inner 
  

   face 
  being 
  glossy. 
  

  

  Fig. 
  1. 
  a, 
  Lithasiopsis 
  Hinkleyi 
  ; 
  b, 
  Lithasia 
  obovata. 
  

  

  Padula 
  similar 
  to 
  that 
  of 
  Ancidosa. 
  The 
  central 
  tooth 
  is 
  short 
  

   and 
  wide, 
  with 
  3, 
  1, 
  3 
  denticles, 
  the 
  body 
  of 
  the 
  tooth 
  smooth 
  below 
  

   the 
  cusps. 
  The 
  adraedian 
  tooth 
  has 
  a 
  very 
  broad, 
  truncate 
  inner 
  

   cusp 
  and 
  two 
  small 
  outer 
  ones. 
  Its 
  body 
  projects 
  at 
  the 
  lower 
  inner 
  

   angle. 
  The 
  inner 
  and 
  outer 
  lateral 
  teeth 
  or 
  uncini 
  have 
  five 
  and 
  

   ten 
  denticles 
  respectively. 
  The 
  shank 
  of 
  the 
  inner 
  uncinus 
  is 
  dilated 
  

   towards 
  its 
  base. 
  

  

  Type. 
  — 
  Z. 
  Hinkleyi. 
  

  

  1 
  Pilsbry 
  & 
  Fernis, 
  Mollusca 
  of 
  the 
  South 
  -Western 
  States, 
  II 
  : 
  Proc. 
  A. 
  N. 
  S. 
  Philad., 
  

   1906, 
  p. 
  167. 
  

  

  