﻿38 
  ON 
  THE 
  NAIADES, 
  

  

  elevated 
  and 
  cleft 
  in 
  the 
  left 
  valve, 
  single 
  and 
  rising 
  from 
  a 
  pit 
  in 
  the 
  

   right; 
  lateral 
  teeth 
  elevated, 
  straight 
  and 
  lamellar; 
  anterior 
  cicatrices 
  

   distinct; 
  posterior 
  cicatrices 
  confluent; 
  dorsal 
  cicatrices 
  within 
  the 
  

   cavity 
  of 
  the 
  shell 
  on 
  the 
  base 
  of 
  the 
  cardinal 
  tooth 
  ; 
  cavity 
  of 
  the 
  

   beaks 
  angular 
  and 
  deep; 
  nacre 
  pearly 
  white 
  and 
  iridescent. 
  

  

  Remarks. 
  — 
  Among 
  the 
  many 
  fine 
  shells 
  presented 
  to 
  the 
  Acade- 
  

   my 
  of 
  Natural 
  Sciences 
  by 
  Mr 
  Schoolcraft 
  from 
  the 
  region 
  of 
  the 
  

   upper 
  lakes, 
  there 
  was 
  a 
  single 
  specimen 
  of 
  the 
  present 
  species. 
  It 
  

   does 
  not 
  seem 
  referable 
  to 
  any 
  described 
  species, 
  and 
  I 
  have 
  conse- 
  

   quently 
  been 
  induced 
  to 
  give 
  it 
  a 
  separate 
  place 
  in 
  the 
  genus. 
  It 
  re- 
  

   sembles 
  most 
  the 
  U. 
  rubiginosus 
  (nobis) 
  in 
  outline, 
  but 
  diners 
  from 
  it 
  

   in 
  being 
  more 
  rounded 
  on 
  the 
  inferior 
  and 
  posterior 
  portions 
  of 
  the 
  

   margins, 
  as 
  well 
  as 
  in 
  the 
  cardinal 
  tooth 
  being 
  more 
  elevated 
  and 
  more 
  

   deeply 
  cleft. 
  In 
  the 
  rays 
  it 
  diners 
  very 
  much 
  from 
  that 
  species. 
  In 
  

   this 
  specimen 
  they 
  are 
  very 
  remarkable, 
  there 
  being 
  a 
  very 
  distinct 
  

   broad 
  one 
  anterior 
  to 
  the 
  umbonial 
  slope, 
  covering 
  one 
  third 
  of 
  the 
  side 
  

   of 
  the 
  disk, 
  and 
  two 
  smaller, 
  posterior 
  to 
  the 
  umbonial 
  slope. 
  When 
  

   there 
  is 
  but 
  a 
  single 
  specimen 
  to 
  describe 
  from, 
  it 
  should 
  be 
  remem- 
  

   bered 
  that 
  many 
  characters 
  are 
  not 
  permanent, 
  and 
  I 
  should 
  not 
  be 
  

   surprised 
  if 
  specimens 
  of 
  this 
  species 
  be 
  found 
  without 
  a 
  single 
  ray, 
  

   although 
  they 
  are 
  so 
  striking 
  in 
  this. 
  The 
  tubercles, 
  which 
  are 
  so 
  

   indistinct, 
  may 
  in 
  other 
  specimens 
  be 
  more 
  distinct 
  and 
  more 
  numerous. 
  

   In 
  this 
  case 
  it 
  will 
  approach 
  so 
  closely 
  to 
  the 
  asperrimus 
  (nobis), 
  that 
  

   it 
  may 
  prove 
  to 
  be 
  only 
  a 
  variety. 
  

  

  Unio 
  geometrtcus. 
  Plate 
  IV. 
  fig. 
  10. 
  

  

  Testd 
  trapezoidali, 
  valde 
  inequilaterali, 
  transversa, 
  compressd 
  ; 
  valvulis 
  tenui- 
  

   bus 
  ; 
  naiibus 
  prominulis, 
  rugis 
  concentricis 
  ; 
  dentibus 
  cardinalibus 
  in 
  valvuld 
  

   utrdque 
  obliquis 
  duplicibusque, 
  lateralibus 
  subrectis 
  ; 
  margaritd 
  purpurea. 
  

  

  Shell 
  trapezoidal, 
  very 
  inequilateral, 
  transverse, 
  compressed 
  ; 
  valves 
  thin 
  ; 
  beaks 
  

   slightly 
  prominent 
  and 
  concentrically 
  wrinkled 
  ; 
  cardinal 
  teeth 
  oblique 
  and 
  double 
  in 
  

   both 
  valves 
  ; 
  lateral 
  teeth 
  nearly 
  straight 
  ; 
  nacre 
  purple. 
  

  

  Hab. 
  Bayou 
  Teche, 
  Louisiana. 
  W. 
  M. 
  Stewart. 
  

  

  