﻿NO. 
  1339. 
  DEEP-WATER 
  MOLLUSCA—VEBRILL 
  AND 
  BUSH. 
  789 
  

  

  forming 
  a 
  small, 
  sunken, 
  heart-shaped, 
  lunular 
  area. 
  Posteriorly 
  

   there 
  is 
  only 
  a 
  faint, 
  depressed 
  undulation, 
  which 
  causes 
  but 
  a 
  slight 
  

   indentation 
  or 
  angulation 
  in 
  the 
  margin; 
  behind 
  this 
  the 
  surface 
  rises 
  

   slightly 
  and 
  forms 
  an 
  inconspicuous 
  ridge 
  surrounding 
  the 
  ligamental 
  

   area, 
  which 
  is 
  long, 
  rather 
  narrow, 
  and 
  sunken, 
  so 
  tliat 
  its 
  margin 
  is 
  

   scarcely 
  visible 
  in 
  a 
  side 
  view. 
  The 
  dorsal 
  margin 
  is 
  a 
  little 
  convex 
  

   and 
  slopes 
  but 
  little, 
  and 
  about 
  equally 
  on 
  both 
  sides 
  of 
  the 
  beak; 
  the 
  

   anterior 
  end 
  is 
  well-rounded 
  and 
  slightly 
  ]>roduced; 
  the 
  ventral 
  margin 
  

   is 
  broadly 
  rounded, 
  a 
  little 
  produced 
  in 
  the 
  middle, 
  and 
  nearly 
  straight 
  

   or 
  very 
  slightly 
  incurved 
  ijosteriorly, 
  opposite 
  the 
  undulation; 
  behind 
  

   this 
  there 
  is 
  a 
  slight 
  obtuse 
  angulation 
  corresiDouding 
  to 
  the 
  ridge 
  below 
  

   the 
  ligamental 
  area. 
  Surfa(;e 
  dull 
  grayish 
  white. 
  The 
  hinge-margin 
  is 
  

   considerably 
  thickened, 
  especially 
  below 
  the 
  beaks 
  and 
  lunular 
  area, 
  

   and 
  a 
  thickened 
  lidge 
  also 
  extends 
  backward 
  beyond 
  the 
  ligamental 
  

   area. 
  There 
  is 
  no 
  distinct 
  tubercle 
  nor 
  tooth 
  like 
  ])rqjection. 
  The 
  

   ])Osterior 
  ligament 
  is 
  unusually 
  strong, 
  and 
  occupies 
  a 
  rather 
  conspicu- 
  

   ous 
  submarginal 
  groove 
  which 
  runs 
  forward 
  under 
  the 
  beak 
  as 
  a 
  thin 
  

   incised 
  line. 
  

  

  Length, 
  4 
  mm. 
  ; 
  height, 
  the 
  same. 
  

  

  Found 
  in 
  8 
  to 
  100 
  fathoms, 
  north 
  of 
  Cape 
  Cod, 
  in 
  the 
  Gulf 
  of 
  Maine, 
  

   Casco 
  Bay, 
  Bay 
  of 
  Fundy, 
  and 
  Halifax 
  Harbor, 
  1872-1885. 
  

  

  CRYPTODON 
  OBSOLETUS, 
  new 
  species. 
  

  

  (Plate 
  LXXXIX, 
  figs. 
  1, 
  2.) 
  

  

  Shell 
  small, 
  higher 
  than 
  long, 
  with 
  the 
  ends 
  and 
  ventral 
  margin 
  

   rounded. 
  Umbos 
  somewhat 
  prominent 
  and 
  swollen; 
  beaks 
  curved 
  

   strongly 
  forward. 
  Posterior 
  plication 
  obsolete, 
  or 
  nearly 
  so, 
  only 
  

   visible 
  in 
  certain 
  positions, 
  and 
  imperfectly 
  defined 
  by 
  a 
  faint 
  undula- 
  

   tion 
  of 
  the 
  surface 
  and 
  margin. 
  The 
  antero-dorsal 
  margin 
  is 
  slightly 
  

   convex 
  in 
  the 
  lunular 
  area, 
  and 
  slopes 
  rapidly 
  to 
  the 
  broadly 
  rounded 
  

   anterior 
  margin 
  with 
  which 
  it 
  forms 
  a 
  very 
  slight 
  and 
  very 
  obtuse 
  

   angle; 
  the 
  whole 
  ventral 
  margin 
  is 
  well-rounded, 
  a 
  little 
  produced 
  in 
  

   the 
  middle; 
  the 
  postero-dorsal 
  margin 
  is 
  broadly 
  convex 
  and 
  ends 
  

   distally 
  in 
  a 
  very 
  obtuse, 
  rounded 
  angle, 
  above 
  which 
  there 
  is 
  a 
  slight 
  

   inbending 
  of 
  the 
  edge. 
  The 
  hinge-plate 
  is 
  rather 
  thick, 
  especially 
  pos- 
  

   teriorly. 
  The 
  ligament 
  is 
  rather 
  strong 
  and 
  considerably 
  curved 
  and 
  

   occupies 
  a 
  narrow, 
  but 
  very 
  distinct 
  groove, 
  mostly 
  within 
  the 
  margin 
  

   posteriorly, 
  and 
  extends 
  forward 
  under 
  and 
  in 
  front 
  of 
  the 
  beaks. 
  The 
  

   anterior 
  hinge-margin 
  is 
  thickened 
  and 
  a 
  little 
  flexuous 
  toward 
  the 
  

   anterior 
  angle 
  of 
  the 
  shell; 
  the 
  proximal 
  end, 
  just 
  under 
  the 
  beak, 
  is 
  

   slightly 
  thickened 
  without 
  forming 
  any 
  apparent 
  tooth. 
  Under 
  the 
  

   microscope, 
  the 
  surface 
  is 
  covered 
  with 
  rather 
  coarse, 
  irregular, 
  con- 
  

   centric 
  undulations, 
  and 
  fine, 
  raised 
  lines 
  of 
  growth, 
  becoming 
  smoother 
  

   at 
  each 
  end, 
  where 
  there 
  are 
  patches 
  of 
  a 
  closely 
  adherent 
  coating 
  of 
  

   red 
  mud 
  and 
  iron 
  oxide. 
  

  

  Length, 
  2.4 
  mm. 
  ; 
  height, 
  2.6 
  mm. 
  

  

  