﻿NO. 
  1139. 
  DEEP-WATER 
  MOLLUSCA—VERRILL 
  AND 
  BUSH. 
  815 
  

  

  horizontal, 
  slightly 
  convex 
  or 
  nearly 
  straight; 
  the 
  ligament 
  is 
  very 
  

   prominent 
  behind 
  the 
  beak, 
  extending 
  backward 
  in 
  a 
  conspicuous 
  

   groove 
  nearly 
  to 
  the 
  posterior 
  end, 
  and 
  terminates 
  anteriorly 
  in 
  a 
  deep 
  

   narrow 
  groove 
  directly 
  under 
  the 
  beak. 
  In 
  the 
  left 
  valve 
  the 
  inner 
  

   edge 
  of 
  the 
  posterior 
  hinge-margin 
  is 
  somewhat 
  sinuous; 
  just 
  behind 
  

   the 
  beaks, 
  opposite 
  the 
  most 
  prominent 
  part 
  of 
  the 
  umbos, 
  it 
  is 
  thick- 
  

   ened 
  and 
  somewhat 
  revolute, 
  decreasing 
  both 
  in 
  thickness 
  and 
  eleva- 
  

   tion 
  to 
  a 
  shallow 
  indentation 
  of 
  the 
  margin 
  ; 
  back 
  of 
  this, 
  it 
  increases 
  

   regularly 
  in 
  thickness 
  and 
  prominence 
  and 
  is 
  again 
  revolute 
  along 
  the 
  

   posterior 
  part 
  of 
  the 
  ligamental 
  furrow. 
  There 
  is 
  no 
  central 
  tooth 
  nor 
  

   any 
  distinct 
  resilium. 
  In 
  the 
  right 
  valve 
  the 
  posterior 
  hinge-margin 
  is 
  

   even 
  more 
  thickened 
  and 
  revolute 
  just 
  back 
  of 
  the 
  beaks, 
  and 
  the 
  in- 
  

   dented, 
  thinner 
  portion, 
  at 
  the 
  end 
  of 
  the 
  prominent 
  part 
  of 
  the 
  liga- 
  

   ment, 
  is 
  more 
  marked. 
  The 
  ligamental 
  groove 
  is 
  consequently 
  less 
  

   conspicuous, 
  being 
  partially 
  concealed 
  by 
  the 
  revolute 
  margin. 
  The 
  

   antero-dorsal 
  margin 
  is 
  compressed 
  and 
  projects 
  strongly 
  upward, 
  

   rising 
  distinctly 
  above 
  the 
  umbos 
  in 
  a 
  side 
  view 
  and 
  is 
  more 
  convex 
  

   than 
  in 
  the 
  left 
  valve. 
  There 
  is 
  also 
  a 
  slight 
  elevation 
  within 
  the 
  dor- 
  

   sal 
  margin 
  directly 
  below 
  the 
  beaks, 
  which 
  might 
  be 
  considered 
  the 
  

   rudiments 
  of 
  a 
  tooth. 
  

  

  The 
  largest 
  specimen, 
  when 
  perfect, 
  would 
  be 
  about 
  15 
  mm, 
  long. 
  

   Two 
  very 
  much 
  broken 
  valves, 
  station 
  2229, 
  N. 
  lat. 
  37o 
  38' 
  40", 
  W. 
  long. 
  

   73° 
  1(V 
  30'', 
  in 
  1,423 
  fathoms, 
  1884, 
  

  

  This 
  species 
  somewhat 
  resembles 
  Cetoclionca 
  nitida 
  (Verrill)i 
  Ball.^ 
  

   It 
  IS 
  however 
  more 
  oblong, 
  with 
  the 
  umbos 
  much 
  smaller 
  and 
  less 
  

   X:)rominent 
  and 
  the 
  beaks 
  less 
  spiral 
  and 
  nearer 
  together. 
  The 
  granu- 
  

   lation 
  of 
  the 
  surface 
  is 
  somewhat 
  stronger 
  and 
  more 
  generally 
  distrib- 
  

   uted. 
  The 
  ligamental 
  groove 
  is 
  longer, 
  deeper, 
  and 
  the 
  ligament 
  itself 
  

   is 
  more 
  prominent 
  behind 
  the 
  beaks. 
  The 
  angulation 
  of 
  the 
  hinge-mar- 
  

   gin 
  of 
  the 
  left 
  valve 
  in 
  a 
  horizontal 
  plane 
  is 
  a 
  peculiar 
  feature 
  not 
  found 
  

   in 
  the 
  other 
  related 
  speci-es 
  and 
  indicates 
  that 
  the 
  valves 
  are 
  decidedly 
  

   unlike 
  in 
  form, 
  but 
  the 
  right 
  valve 
  is 
  too 
  much 
  broken 
  to 
  show 
  the 
  

   anterior 
  margin, 
  

  

  CETOMYA 
  species. 
  

  

  A 
  broken 
  left 
  valve 
  {^o. 
  52013) 
  from 
  station 
  2481, 
  I^. 
  lat. 
  44° 
  7' 
  30", 
  

   W, 
  long, 
  57° 
  IG' 
  45", 
  in 
  116 
  fathoms, 
  resembles 
  Poromya 
  {Cetomya) 
  

   elongata 
  Ball, 
  from 
  the 
  West 
  Indies 
  and 
  Barbados, 
  in 
  100 
  to 
  119 
  fath- 
  

   oms. 
  It 
  is, 
  however, 
  too 
  incomplete 
  for 
  determination 
  without 
  direct 
  

   comparison 
  with 
  authentic 
  specimens. 
  

  

  It 
  is 
  larger 
  and 
  more 
  strongly 
  truncate 
  i)osteriorly 
  than 
  Poromya 
  

   gramdata 
  (Xyst) 
  Forbes 
  and 
  Hanley, 
  and 
  the 
  granules 
  are 
  coarser 
  and 
  

   not 
  so 
  numerous. 
  It 
  differs, 
  moreover, 
  very 
  strongly 
  in 
  the 
  hinge 
  

   characters, 
  for 
  the 
  hinge-plate 
  is 
  much 
  thinner 
  and 
  the 
  large 
  tooth 
  in 
  

   the 
  left 
  valve 
  is 
  wanting 
  in 
  our 
  species. 
  

  

  1 
  Thracia 
  nitida 
  Verrill, 
  Trans. 
  Conn. 
  Acad., 
  VI, 
  p. 
  221, 
  pi. 
  xxxii, 
  fig. 
  22, 
  1884. 
  

   - 
  Cetochonca 
  nitida 
  Dall, 
  Bull. 
  Miis. 
  Coinp. 
  Zofil., 
  XII, 
  p. 
  281, 
  1886. 
  

  

  