﻿788 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  vouxx. 
  

  

  4.5 
  mm.; 
  lieiglit, 
  5.25 
  mm. 
  In 
  this 
  the 
  anterior 
  or 
  upper 
  plication 
  is 
  

   mucli 
  less 
  distinct 
  than 
  in 
  the 
  type, 
  and 
  it 
  is 
  therefore 
  possible 
  that 
  

   this 
  feature 
  is 
  abnormal. 
  

  

  CRYPTODON 
  EQUALIS, 
  new 
  species. 
  

   (Plate 
  XCI, 
  figs. 
  5, 
  6.) 
  

  

  Shell 
  of 
  moderate 
  size, 
  grayish 
  white, 
  rather 
  swollen, 
  pyriform, 
  usu- 
  

   ally 
  a 
  little 
  higher 
  than 
  long, 
  but 
  sometimes 
  the 
  height 
  aud 
  length 
  are 
  

   about 
  equal. 
  Umbos 
  rather 
  prominent; 
  beaks 
  median, 
  conspicuously 
  

   raised 
  above 
  the 
  margin 
  and 
  curved 
  strongly 
  forward 
  so 
  as 
  to 
  produce 
  

   a 
  rather 
  deep, 
  broad, 
  cordate, 
  but 
  ill 
  defined 
  Innuhir 
  area. 
  Anterior 
  

   and 
  jiosterior 
  ends 
  nearly 
  equal. 
  The 
  dorsal 
  margin 
  slopes 
  rapidly 
  on 
  

   both 
  sides 
  of 
  the 
  beak; 
  anteriorly, 
  in 
  the 
  lunular 
  region, 
  it 
  is 
  nearly 
  

   straight; 
  the 
  anterior 
  end 
  is 
  pretty 
  evenly 
  rounded, 
  foruiing 
  a 
  continu- 
  

   ous 
  curve 
  with 
  the 
  ventral 
  margin, 
  which 
  forms 
  nearly 
  a 
  semicircular 
  

   curve; 
  the 
  posterior 
  end 
  has 
  one 
  broad, 
  shallow 
  undulation 
  which 
  

   causes 
  a 
  slight 
  incurvature 
  in 
  the 
  postero-ventral 
  margin; 
  above 
  this 
  

   the 
  dorsal 
  margin 
  is 
  very 
  slightly 
  convex 
  and 
  forms 
  an 
  angle 
  at 
  the 
  

   commencement 
  of 
  the 
  fold. 
  The 
  ligameutal 
  area 
  is 
  marked 
  by 
  a 
  smooth, 
  

   long, 
  lanceolate, 
  slightly 
  sunken 
  portion, 
  clearly 
  separated 
  by 
  an 
  

   incised 
  line. 
  The 
  general 
  surface 
  is 
  covered 
  with 
  slightly 
  marked, 
  

   more 
  or 
  less 
  irregular 
  lines 
  of 
  growth. 
  The 
  hinge-margin 
  is 
  moderately 
  

   thickened 
  and 
  is 
  essentially 
  the 
  same 
  in 
  both 
  valves. 
  There 
  is 
  a 
  Avell 
  

   marked 
  swelling 
  both 
  before 
  and 
  behind 
  the 
  beak 
  and 
  a 
  more 
  con- 
  

   spicuous 
  one 
  immediately 
  under 
  it; 
  a 
  less 
  conspicuous 
  thickening, 
  with 
  

   its 
  external 
  edge 
  excurved, 
  extends 
  along 
  the 
  postero-dorsal 
  margin, 
  

   in 
  the 
  ligameutal 
  region. 
  Muscular 
  and 
  pallial 
  scars 
  indistinct. 
  

  

  Length, 
  5 
  mm.; 
  height, 
  5i 
  mm.; 
  thickness, 
  4 
  mm. 
  Some 
  specimens 
  

   are 
  somewhat 
  larger 
  than 
  this. 
  

  

  In 
  the 
  large 
  series 
  which 
  we 
  have 
  of 
  this 
  species 
  there 
  is 
  some 
  

   variation. 
  In 
  some 
  cases 
  the 
  form 
  is 
  less 
  swollen, 
  the 
  length 
  is 
  

   slightly 
  in 
  excess 
  of 
  the 
  height, 
  so 
  that 
  the 
  general 
  outline 
  is 
  more 
  

   evenly 
  rounded. 
  The 
  species 
  is, 
  however, 
  notable 
  for 
  the 
  equality" 
  of 
  

   the 
  anterior 
  and 
  jjosterior 
  ends 
  and 
  the 
  presence 
  of 
  the 
  single 
  slight 
  

   undulation. 
  Cri/ptodon 
  gonldii 
  somewhat 
  resembles 
  this 
  species, 
  but 
  

   diflers 
  in 
  being 
  longer 
  iu 
  pro]>oi 
  tion 
  to 
  its 
  height, 
  in 
  its 
  more 
  com- 
  

   pressed 
  form, 
  and 
  in 
  having 
  two 
  distinct 
  folds 
  or 
  undulations. 
  It 
  is 
  

   also 
  closely 
  allied 
  to 
  C.flextiosns 
  of 
  Euroi)e, 
  but 
  is 
  more 
  pyriform 
  in 
  

   shape 
  and 
  lacks 
  the 
  anterior 
  angulation 
  noticeable 
  in 
  that 
  species. 
  

  

  Taken 
  at 
  thirty-two 
  stations, 
  between 
  N. 
  lat. 
  47° 
  40', 
  W. 
  long. 
  47° 
  35' 
  

   30", 
  and 
  N. 
  lat. 
  37° 
  08', 
  W. 
  -long. 
  74° 
  33', 
  in 
  04 
  to 
  1,537 
  fathoms, 
  1873- 
  

   1886. 
  

  

  CRYPTODON 
  PLANUS, 
  new 
  species. 
  

  

  (Plate 
  LXXXVIII, 
  tigs. 
  3, 
  4.) 
  

  

  Shell 
  small, 
  well-rounded, 
  the 
  length 
  and 
  height 
  about 
  equal, 
  with 
  

   the 
  beak 
  small, 
  prominent, 
  nearly 
  central, 
  curved 
  strongly 
  forward, 
  

  

  