﻿83G 
  rUOCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  

  

  HYALOPECTEN 
  DILECTUS 
  Verrill 
  and 
  Bush. 
  

  

  (I'late 
  XCVII, 
  fig. 
  9.) 
  

  

  TTyalopectcn 
  dileelns 
  Vkukim. 
  and 
  Hush, 
  \u 
  Vkrkill, 
  Trants. 
  ('onu. 
  Afii<l., 
  X, 
  pj). 
  

   80, 
  92, 
  1897. 
  

  

  Shell 
  small, 
  tliiii, 
  fragile, 
  strongly 
  undulated, 
  slightly 
  oblique, 
  with 
  

   the 
  ventral 
  margin 
  broadl}^ 
  rounded, 
  dorsal 
  margin 
  straight. 
  In 
  the 
  

   right 
  valve 
  the 
  anterior 
  auricle 
  is 
  rather 
  narrow, 
  elongated, 
  with 
  a 
  

   deep 
  angular 
  notch 
  beneath; 
  the 
  posterior 
  auricle 
  is 
  shorter, 
  with 
  a 
  

   prominent 
  dorsal 
  angle 
  which 
  is 
  less 
  than 
  a 
  right 
  angle, 
  owing 
  to 
  the 
  

   emargination 
  of 
  the 
  posterior 
  end. 
  In 
  the 
  left 
  valve 
  the 
  anterior 
  auri- 
  

   cle 
  is 
  broad, 
  with 
  its 
  i)Osterior 
  end 
  nearly 
  rectilinear, 
  and 
  forms 
  a 
  right 
  

   angle 
  with 
  the 
  dorsal 
  margin; 
  the 
  posterior 
  auricle 
  has 
  a 
  slightly 
  

   ])roniinent 
  dorsal 
  angle 
  and 
  X'osterior 
  emargination 
  as 
  in 
  the 
  right 
  valve. 
  

   The 
  beaks 
  are 
  a 
  little 
  prominent 
  and 
  project 
  somewhat 
  above 
  the 
  dor- 
  

   sal 
  margin, 
  more 
  in 
  the 
  upper 
  or 
  left 
  valve. 
  The 
  surface 
  in 
  both 
  valves 
  

   is 
  covered 
  with 
  broad 
  and 
  rather 
  regular 
  undulations, 
  which 
  are 
  most 
  

   prominent 
  in 
  the 
  left 
  valve, 
  and 
  are 
  crossed 
  by 
  regular, 
  well 
  spaced, 
  

   thin, 
  raised,' 
  radial 
  lines,, 
  which 
  become 
  fine 
  and 
  more 
  crowded 
  at 
  the 
  

   ends 
  of 
  the 
  valve; 
  they 
  are 
  nearly 
  obsolete 
  in 
  the 
  right 
  valve, 
  being 
  

   represented 
  by 
  microscopic 
  strise. 
  In 
  both 
  valves 
  the 
  anterior 
  auricle 
  

   is 
  marked 
  by 
  several 
  fine, 
  rough, 
  radial 
  ridges 
  which 
  are 
  stronger 
  and 
  

   more 
  numerous 
  in 
  the 
  left 
  valve. 
  The 
  interior 
  is 
  strongly 
  undulated, 
  

   and 
  the 
  left 
  valve 
  is 
  marked 
  by 
  distinct, 
  radial 
  grooves. 
  Ilesilium 
  

   small, 
  central. 
  Color 
  yellow, 
  or 
  dirty 
  white. 
  

  

  Length, 
  8 
  mm. 
  ; 
  height, 
  the 
  same. 
  

  

  One 
  live, 
  imperfect 
  specimen 
  (lUo. 
  52539), 
  station 
  2570, 
  off 
  Marthas 
  

   Viiieyard, 
  in 
  1,813 
  fathoms, 
  1885. 
  

  

  This 
  species 
  is 
  closely 
  allied 
  to 
  Hynlopecten 
  fragiUs 
  (Jeffreys) 
  and 
  

   resembles 
  very 
  nearly 
  his 
  figure,' 
  which 
  probably 
  represents 
  a 
  species 
  

   distinct 
  from 
  the 
  original 
  type 
  described 
  by 
  him, 
  and 
  may 
  be 
  identical 
  

   with 
  our 
  shell. 
  The 
  latter 
  differs 
  decidedly 
  from 
  the 
  original 
  descrip 
  

   tion 
  of 
  if. 
  fragilis. 
  Moreover, 
  we 
  have 
  obtained 
  from 
  several 
  stations 
  

   a 
  shell 
  of 
  similar 
  size 
  which 
  appears 
  to 
  be 
  the 
  true 
  fragilis,- 
  as 
  it 
  agrees 
  

   closely 
  with 
  the 
  description. 
  Hyalopevten 
  pudicus 
  (Smith) 
  from 
  east 
  of 
  

   Marion 
  Island, 
  in 
  1,375 
  fathoms, 
  is 
  a 
  closely 
  related 
  species, 
  as 
  is 
  also 
  

   Hyalopecten 
  undatus 
  Verrill. 
  

  

  These 
  four 
  species 
  agree 
  in 
  having 
  the 
  valves 
  thin 
  and 
  translucent 
  

   and 
  sculptured 
  with 
  distinct 
  concentric 
  undulations, 
  while 
  the 
  radial 
  

   sculpture 
  does 
  not 
  form 
  strong 
  ribs. 
  They 
  seem 
  to 
  be 
  related 
  to 
  the 
  

   genus 
  or 
  subgenus 
  Sgnrydonema 
  Meek, 
  which 
  was 
  based 
  on 
  a 
  creta- 
  

   ceous 
  species 
  and 
  has 
  not 
  hitherto 
  been 
  reported 
  as 
  still 
  living. 
  But 
  

   the 
  exact 
  characters 
  of 
  the 
  typical 
  fossil 
  species 
  are 
  not 
  yet 
  known. 
  

  

  I 
  Proc. 
  Zoo]. 
  Soc, 
  London, 
  pi. 
  XLV, 
  tig. 
  1, 
  June, 
  1879. 
  

  

  '■^Thc 
  true 
  Hyalopecten 
  fragilis 
  (Jt'ftreys) 
  was 
  taken 
  at 
  five 
  stations 
  between 
  N. 
  lat. 
  

   40' 
  6', 
  W. 
  long. 
  68'^ 
  1' 
  30", 
  and 
  N. 
  lat. 
  35° 
  49' 
  30", 
  W. 
  long. 
  74° 
  34' 
  45", 
  in 
  578 
  to 
  1,525 
  

   fathoms, 
  1883-1886. 
  

  

  