﻿NO. 
  1139. 
  DEEP-WATER 
  MOLLUSC 
  J— 
  FERRILL 
  AND 
  BUSH. 
  835 
  

  

  It 
  is 
  probable, 
  however, 
  that 
  it 
  grows 
  to 
  a 
  much 
  hirger 
  size 
  thau 
  any 
  

   of 
  the 
  specimens 
  obtained. 
  

  

  It 
  is 
  named 
  in 
  honor 
  of 
  Mr. 
  James 
  E. 
  Benedict, 
  for 
  several 
  years 
  

   zoologist 
  in 
  charge 
  on 
  the 
  steamer 
  Albatross, 
  througli 
  wliose 
  care 
  and 
  

   great 
  interest 
  so 
  many 
  small 
  species 
  were 
  brought 
  to 
  light. 
  

  

  CHLAMYS 
  COSTELLATA 
  Verrill 
  and 
  Bush. 
  

  

  (Plate 
  LXXXVI, 
  flg. 
  6.) 
  

  

  Chlamys 
  costellata 
  Vekrill 
  and 
  Bush, 
  in 
  Veiikill, 
  Trans. 
  Conn. 
  Acad., 
  X, 
  pp. 
  75, 
  

   91, 
  1897. 
  

  

  Shell 
  small, 
  thin, 
  translucent, 
  bluish 
  white, 
  covered 
  on 
  both 
  valves 
  

   with 
  continuous, 
  elevated 
  and 
  somewhat 
  thickened, 
  well-separated, 
  

   radiating- 
  riblets, 
  of 
  wliich 
  there 
  are 
  more 
  than 
  thirty 
  in 
  the 
  left 
  valve 
  

   of 
  tlie 
  largest 
  example. 
  Length 
  of 
  the 
  shell 
  considerably 
  less 
  than 
  its 
  

   height. 
  Dorsal 
  hinge-margin 
  elongated, 
  especially 
  on 
  the 
  anterior 
  end. 
  

   In 
  the 
  light 
  valve 
  the 
  anterior 
  auricle 
  is 
  considerably 
  elongated, 
  

   obtusely 
  rounded 
  or 
  subtruncated 
  at 
  the 
  end, 
  with 
  a 
  wide, 
  angular 
  

   byssal 
  notch 
  beneath 
  it, 
  having 
  two 
  or 
  three 
  pectinidial 
  teeth; 
  it 
  has 
  

   a 
  broad, 
  smooth, 
  angular 
  area 
  next 
  the 
  body 
  of 
  the 
  shell, 
  above 
  wliich 
  

   there 
  are 
  three 
  well-marked, 
  angular, 
  radial 
  ridges, 
  separated 
  by 
  wider 
  

   concave 
  interspaces; 
  the 
  posterior 
  auricle 
  is 
  small, 
  triangular, 
  the 
  outer 
  

   corner 
  forming 
  a 
  little 
  more 
  thau 
  a 
  right 
  angle, 
  and 
  the 
  posterior 
  mar- 
  

   gin 
  nearly 
  straight, 
  without 
  any 
  distinct 
  notch. 
  The 
  dorsal 
  margins 
  of 
  

   the 
  body 
  of 
  the 
  shell 
  are 
  nearly 
  straight 
  and 
  diverge 
  at 
  less 
  than 
  a 
  

   right 
  angle; 
  the 
  ventral 
  margin 
  is 
  pretty 
  evenly 
  rounded, 
  a 
  little 
  

   produced 
  in 
  the 
  middle. 
  The 
  beak 
  is 
  small, 
  acute, 
  appressed, 
  and 
  does 
  

   not 
  project 
  beyond 
  the 
  margin. 
  The 
  radial 
  libs 
  are 
  very 
  distinct, 
  clean 
  

   cut, 
  thickened, 
  rounded 
  at 
  the 
  summit, 
  separated 
  by 
  nearly 
  smooth 
  

   intervals, 
  two 
  or 
  three 
  times 
  as 
  broad 
  as 
  the 
  ribs 
  themselves; 
  the 
  ribs 
  

   increase 
  regularly 
  in 
  width 
  from 
  near 
  the 
  umbo 
  to 
  the 
  margin; 
  a 
  few 
  

   intermediate 
  ridges 
  commence 
  near 
  the 
  margin. 
  The 
  left 
  valve 
  is 
  

   badly 
  broken; 
  it 
  is, 
  however, 
  somewhat 
  more 
  convex 
  than 
  the 
  other, 
  

   and 
  the 
  radial 
  ribs 
  are 
  crossed 
  by 
  numerous 
  concentric 
  striations 
  giving 
  

   them 
  a 
  linely 
  crenulated 
  or 
  beaded 
  appearance; 
  the 
  anterior 
  auricle 
  is 
  

   broad, 
  triangular, 
  the 
  outer 
  end 
  slightly 
  rounded, 
  with 
  a 
  slight 
  incurved 
  

   notch 
  below; 
  it 
  is 
  crossed 
  by 
  about 
  six 
  small, 
  radial 
  ribs, 
  similar 
  to 
  

   those 
  on 
  the 
  body 
  of 
  the 
  shell; 
  raised 
  lines 
  of 
  growth 
  also 
  occur 
  at 
  

   irregular 
  intervals. 
  Inner 
  surface 
  smooth 
  and 
  lustrous, 
  showing 
  the 
  

   grooves 
  corresponding 
  to 
  the 
  external 
  ribs 
  and 
  also 
  a 
  very 
  distinct 
  

   microscopic 
  structure, 
  but 
  it 
  is 
  destitute 
  of 
  radial 
  line. 
  Internally, 
  the 
  

   hinge 
  margin 
  is 
  thin 
  and 
  narrow, 
  with 
  a 
  sharply 
  impressed, 
  submar- 
  

   ginal 
  groove 
  on 
  each 
  side; 
  the 
  resilial 
  pit 
  is 
  excavated 
  in 
  the 
  margin 
  

   of 
  the 
  hinge 
  itself; 
  the 
  anterior 
  auricle 
  has 
  internal 
  grooves 
  corres] 
  ond- 
  

   ing 
  to 
  the 
  external 
  ribs. 
  

  

  Length 
  of 
  the 
  largest 
  specimen, 
  (I 
  mm. 
  ; 
  height, 
  6.5 
  mm. 
  

  

  Three 
  live 
  specimens, 
  at 
  two 
  stations, 
  off 
  the 
  Grand 
  Banks, 
  in 
  07 
  to 
  

   72 
  fathoms, 
  1885-86. 
  

  

  