﻿48 
  

  

  PROOEKDINGS 
  OF 
  THK 
  MALA.COLOGICAL 
  .SOCIKXl'. 
  

  

  Shells 
  of 
  this 
  genus 
  have 
  the 
  heavily 
  calloused 
  inaer 
  lip 
  of 
  

   Lithasia, 
  but 
  differ 
  from 
  that 
  genus 
  by 
  the 
  operculum, 
  which 
  in 
  

   Lithcma 
  is 
  oblong 
  with 
  almost 
  basal 
  nucleus 
  (fig. 
  \h, 
  L. 
  ohovata, 
  Say). 
  

   Some 
  forms 
  of 
  the 
  heterogeneous 
  group 
  Goniohasis 
  have 
  a 
  similar 
  

   operculum, 
  but 
  they 
  differ 
  by 
  the 
  thin 
  parietal 
  callus. 
  Lithasiopsis 
  

   is 
  not 
  unlike 
  Melanopsis 
  in 
  the 
  calloused 
  columella, 
  but 
  it 
  differs 
  in 
  

   important 
  features 
  of 
  the 
  dentition. 
  In 
  dentition 
  Lithasiopsis 
  stands 
  

   nearest 
  Ancxdosa, 
  which 
  it 
  resembles 
  in 
  having 
  the 
  inner 
  cusp 
  of 
  the 
  

   adraedian 
  tooth 
  enormously 
  developed. 
  

  

  ^^p^N^J^ 
  

  

  Fig. 
  2. 
  Lithasiopsis 
  ITinldeyi. 
  

  

  Lithasiopsis 
  inhabits 
  streams 
  tributary 
  to 
  the 
  Panuco 
  River. 
  This 
  

   river 
  system 
  has 
  one 
  of 
  the 
  richest 
  faunas 
  of 
  freshwater 
  shells 
  in 
  

   Mexico. 
  Mr. 
  Hinkley's 
  researches 
  have 
  brought 
  to 
  light 
  a 
  con- 
  

   siderable 
  number 
  of 
  Unionida3 
  ; 
  a 
  fine 
  group 
  of 
  Pachycheili, 
  including 
  

   several 
  globose 
  forms 
  like 
  Paludomus 
  ; 
  species 
  of 
  Somatogi/rus, 
  

   Amm'cola, 
  Potamopyrgiis, 
  Cochliopa^ 
  Emrnerioia, 
  Pterides, 
  and 
  Gund- 
  

   lachia, 
  etc. 
  Except 
  the 
  Lymnaeidae 
  most 
  of 
  the 
  species 
  are 
  unknown 
  

   elsewhere, 
  but 
  a 
  few 
  extend 
  as 
  far 
  south 
  as 
  Vera 
  Cruz, 
  and 
  some 
  

   others 
  north 
  to 
  the 
  E,io 
  Grande. 
  

  

  Lithasiopsis 
  Hinkleyi, 
  n.sp. 
  Pigs. 
  \a, 
  2, 
  3. 
  

  

  The 
  shell 
  is 
  cylindric, 
  or 
  oval 
  cylindric, 
  with 
  a 
  short 
  acute 
  spire 
  

   with 
  concave 
  outlines 
  ; 
  solid, 
  dull 
  yellow 
  or 
  greenish-yellow. 
  The 
  

   first 
  1^ 
  whorls 
  are 
  smooth, 
  glossy, 
  and 
  convex 
  ; 
  the 
  following 
  1^ 
  to 
  2|- 
  

   whorls 
  dull, 
  only 
  slightly 
  convex, 
  showing 
  a 
  keel 
  or 
  thread 
  above 
  

   or 
  in 
  the 
  suture 
  below. 
  In 
  the 
  typical 
  form 
  the 
  following 
  whorl 
  

   has 
  an 
  acute 
  median 
  spiral 
  thread. 
  The 
  penultimate 
  and 
  next 
  earlier 
  

   whorls 
  bear 
  three 
  strong 
  spirals, 
  and 
  these 
  continue 
  upon 
  the 
  last 
  

   whorl, 
  which 
  has 
  a 
  group 
  of 
  spiral 
  cords 
  at 
  the 
  shoulder, 
  is 
  smooth 
  

   and 
  flat 
  or 
  concave 
  in 
  the 
  middle, 
  and 
  has 
  weak 
  spiral 
  cords 
  on 
  the 
  

   base. 
  (In 
  the 
  smooth 
  form 
  the 
  later 
  whorls 
  are 
  without 
  spiral 
  

   sculpture, 
  and 
  it 
  may 
  be 
  very 
  weak 
  or 
  almost 
  wanting 
  on 
  the 
  spire.) 
  

  

  