﻿792 
  PEOCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  vol.xx. 
  

  

  before 
  and 
  behind 
  the 
  beaks, 
  but 
  there 
  is 
  no 
  tooth-like 
  i)rominence 
  at 
  

   any 
  point. 
  

  

  Length, 
  about 
  3.1 
  mm. 
  ; 
  height, 
  about 
  3 
  mm. 
  

  

  One 
  imperfect 
  specimen, 
  station 
  1093, 
  X. 
  lat. 
  39° 
  56', 
  W. 
  long. 
  69^ 
  

   45', 
  in 
  349 
  fathoms, 
  1882. 
  

  

  This 
  species 
  is 
  remarkable 
  for 
  the 
  plainness 
  of 
  its 
  surface, 
  and 
  the 
  

   simplicity 
  of 
  its 
  hinge, 
  as 
  it 
  has 
  neither 
  radial 
  undulations 
  nor 
  tooth- 
  

   like 
  projections 
  on 
  the 
  hinge-margin. 
  In 
  form 
  it 
  greatly 
  resembles 
  

   Axinopsis 
  orhieidata, 
  but 
  lacks 
  the 
  conspicuous 
  concavity 
  in 
  the 
  

   antero-dorsal 
  margin. 
  It 
  has, 
  however, 
  a 
  very 
  obvious 
  posterior 
  liga- 
  

   mental 
  furrow 
  in 
  the 
  same 
  relative 
  position 
  as 
  that 
  of 
  other 
  species 
  of 
  

   Cryptodon. 
  

  

  A 
  single 
  valve 
  taken 
  at 
  Eastport, 
  Maine, 
  1872, 
  agrees 
  closely 
  with 
  

   the 
  type 
  in 
  form, 
  but 
  is 
  somewhat 
  less 
  thin 
  and 
  hyaline 
  and 
  the 
  beaks 
  

   are 
  a 
  trifle 
  more 
  prominent. 
  The 
  surface 
  has 
  faint 
  and 
  rather 
  distant 
  

   concentric 
  undulations, 
  visible 
  only 
  under 
  the 
  microscope, 
  being 
  most 
  

   distinct 
  on 
  the 
  umbo. 
  The 
  microscopic 
  striations 
  are 
  a 
  little 
  more 
  dis- 
  

   tinct 
  and 
  in 
  some 
  lights 
  give 
  to 
  the 
  surface 
  a 
  tibrous 
  or 
  finely 
  vermic- 
  

   ulate 
  appearance 
  when 
  highly 
  magnified. 
  This 
  character, 
  however, 
  

   has 
  been 
  noticed 
  in 
  other 
  species. 
  The 
  hinge-margin 
  is 
  a 
  little 
  more 
  

   thickened 
  and 
  has 
  a 
  minute 
  swelling 
  on 
  the 
  inner 
  margin 
  just 
  beneath 
  

   the 
  beak, 
  scarcely 
  worthy 
  the 
  name 
  of 
  tooth; 
  the 
  ligamental 
  groove 
  is 
  

   also 
  somewhat 
  more 
  strongly 
  marked. 
  This 
  may 
  prove 
  to 
  be 
  a 
  distinct 
  

   species 
  more 
  nearly 
  related 
  to 
  Axinopsis 
  orhiculata 
  from 
  which 
  it 
  differs 
  

   in 
  having 
  the 
  antero-dorsal 
  margin 
  convex 
  instead 
  of 
  strongly 
  concave, 
  

   and 
  the 
  general 
  outline 
  more 
  evenly 
  rounded, 
  and 
  a 
  less 
  evident 
  tooth- 
  

   like 
  thickening 
  of 
  the 
  hinge 
  margin. 
  

  

  Length, 
  about 
  2.8 
  mm. 
  ; 
  height, 
  about 
  2.6 
  ram. 
  

  

  CRYPTODON 
  (AXINULUS) 
  PYGM^EUS, 
  new 
  species. 
  

  

  (Plate 
  LXXXVI, 
  figs. 
  3, 
  4.) 
  

  

  Shell 
  minute, 
  somewhat 
  compressed, 
  transversely 
  ovate, 
  inequi- 
  

   lateral, 
  with 
  the 
  anterior 
  end 
  the 
  longer, 
  and 
  with 
  a 
  slightly 
  produced 
  

   posterior 
  angulation. 
  Surface 
  scarcely 
  lustrous, 
  covered 
  with 
  fine 
  

   lines 
  of 
  growth 
  and 
  microscopic 
  striations, 
  and 
  more 
  or 
  less 
  incrusted 
  

   with 
  ferruginous 
  mud, 
  especially 
  posteriorly; 
  there 
  is 
  barely 
  a 
  trace 
  of 
  

   a 
  posterior 
  fold. 
  Umbos 
  a 
  little 
  prominent, 
  beaks 
  small, 
  slightly 
  

   raised 
  above 
  the 
  margin, 
  and 
  turned 
  a 
  little 
  forward. 
  The 
  antero- 
  

   dorsal 
  margin 
  is 
  nearly 
  straight, 
  or 
  sometimes 
  slightly 
  convex, 
  with 
  a 
  

   slightly 
  excavated, 
  small, 
  lunular 
  area; 
  the 
  anterior 
  end 
  is 
  broad, 
  con- 
  

   siderably 
  produced, 
  and 
  evenly 
  rounded; 
  the 
  ventral 
  margin 
  is 
  broadly 
  

   rounded, 
  not 
  at 
  all 
  produced, 
  and 
  joins 
  the 
  posterior 
  margin 
  in 
  a 
  small 
  

   obtuse 
  angulation, 
  above 
  which 
  the 
  dorsal 
  margin 
  is 
  slightly 
  convex 
  

   and 
  slopes 
  rapidly 
  from 
  the 
  beaks. 
  

  

  The 
  inner 
  surface 
  is 
  smooth 
  with 
  inconspicuous 
  muscular 
  scars. 
  

  

  