﻿790 
  PROCEEDINGS 
  OF 
  TEE 
  NATIONAL 
  MUSEUM. 
  

  

  Four 
  specimens, 
  at 
  three 
  stations, 
  off 
  Marthas 
  Vineyard, 
  in 
  100 
  to 
  

   390 
  fathoms, 
  1880-1885. 
  

  

  AXINULUS, 
  new 
  subgenus 
  or 
  genus 
  

  

  Type. 
  — 
  Aximilvfi 
  hreins, 
  new 
  species. 
  

  

  We 
  propose 
  this 
  division 
  to 
  include 
  those 
  species 
  which 
  agree 
  with 
  

   Cryptodon 
  in 
  the 
  character 
  of 
  the 
  hinge 
  and 
  ligament, 
  but 
  lack 
  the 
  

   plications 
  of 
  the 
  shell, 
  and 
  have, 
  therefore, 
  a 
  smaller 
  posterior 
  adductor 
  

   muscle. 
  

  

  CRYPTODON 
  (AXINULUS) 
  BREVIS, 
  new 
  species 
  

   (Plate 
  LXXXIX, 
  ligs. 
  7, 
  8.) 
  

  

  Shell 
  small, 
  short, 
  the 
  height 
  exceeding 
  the 
  length, 
  somewhat 
  pyri- 
  

   form, 
  with 
  slightly 
  prominent 
  umbos 
  and 
  small 
  subcentral 
  beaks, 
  which 
  

   are 
  but 
  little 
  i)roniinent 
  and 
  turn 
  forward. 
  The 
  antero 
  and 
  i)ostero- 
  

   dorsal 
  margins 
  are 
  about 
  e(]ual 
  in 
  length, 
  the 
  latter 
  slightly 
  more 
  

   broadly 
  rounded 
  than 
  the 
  former, 
  which 
  is 
  a 
  little 
  incurved 
  near 
  the 
  

   beak 
  so 
  as 
  to 
  form 
  a 
  very 
  slight 
  luiuilar 
  area; 
  both 
  ends 
  are 
  broadly 
  

   rounded 
  and 
  nearly 
  equal; 
  the 
  ventral 
  margin 
  is 
  slightly 
  convex 
  and 
  a 
  

   little 
  produced 
  just 
  in 
  front 
  of 
  the 
  middle; 
  an 
  exceedingly 
  faint, 
  

   scarcely 
  discernible 
  undulation 
  runs 
  from 
  the 
  beak 
  to 
  the 
  posterior 
  

   ventral 
  margin. 
  The 
  surface 
  is 
  covered 
  with 
  very 
  tine, 
  close, 
  parallel 
  

   lines 
  of 
  growth 
  visible 
  only 
  when 
  much 
  magnified. 
  Grains 
  of 
  tine 
  fer- 
  

   ruginous 
  sand 
  or 
  mud 
  usually 
  adhere 
  closely 
  to 
  the 
  surface, 
  both 
  ante- 
  

   riorly 
  and 
  posteriorly. 
  The 
  posterior 
  ligament 
  is 
  well 
  developed 
  and 
  

   occupies 
  a 
  well-marked 
  marginal 
  groove: 
  a 
  small, 
  thickened, 
  more 
  

   internal 
  portion, 
  situated 
  Just 
  behind 
  the 
  beak, 
  within 
  the 
  margin, 
  

   appears 
  to 
  be 
  continuous 
  with 
  the 
  external 
  ligament. 
  The 
  inner 
  edge 
  

   of 
  the 
  dorsal 
  margin 
  is 
  slightly 
  thickened, 
  for 
  a 
  short 
  distance, 
  just 
  in 
  

   front 
  of 
  the 
  beak. 
  

  

  Length, 
  2^ 
  mm.; 
  height, 
  2.5 
  mm. 
  

  

  Several 
  live 
  specimens 
  and 
  separate 
  valves 
  were 
  found 
  at 
  six 
  sta- 
  

   tions, 
  between 
  i^. 
  lat. 
  40° 
  16' 
  50", 
  W. 
  long. 
  67° 
  5' 
  15", 
  and 
  Is^. 
  lat. 
  38° 
  

   22', 
  W. 
  long. 
  70° 
  17' 
  30", 
  in 
  984 
  to 
  1,825 
  fathoms, 
  1883-1880. 
  

  

  At 
  station 
  2208 
  was 
  found 
  a 
  single 
  imperfect 
  valve 
  closely 
  resem- 
  

   bling 
  this 
  species 
  but 
  of 
  much 
  larger 
  size. 
  

  

  Length, 
  5.5 
  mm. 
  ; 
  height, 
  G.5 
  mm. 
  

  

  It 
  is, 
  however, 
  much 
  less 
  regular 
  in 
  outline, 
  having 
  a 
  nearly 
  straight, 
  

   rapidly 
  sloping 
  antero 
  dorsal 
  margin, 
  merging 
  very 
  abruptly 
  into 
  the 
  

   broadly 
  and 
  very 
  slightly 
  curved 
  and 
  sloping 
  anterior 
  margin, 
  forming 
  

   a 
  somewhat 
  angular 
  and 
  little 
  produced 
  anterior 
  end; 
  ventral 
  margin 
  

   strongly 
  convex, 
  curving 
  gradually 
  into 
  the 
  posterior 
  margin 
  which 
  

   slopes 
  rapidly 
  from 
  the 
  beak; 
  postero-dorsal 
  margin 
  is 
  convex 
  but 
  

   rises 
  only 
  a 
  little 
  above 
  the 
  outline 
  of 
  the 
  distinct 
  ridge 
  which 
  borders 
  

   the 
  ligamental 
  area. 
  

  

  