﻿NO. 
  1139. 
  DEEP-WATER 
  MOLLUSCA—VEBEILL 
  AND 
  BUSH. 
  871 
  

  

  YOLDIELLA 
  SUBEQUILATERA 
  (Jeffreys). 
  

  

  Leda 
  suiequilatera 
  Jeffrkys, 
  Proc. 
  Zool. 
  Soc, 
  London, 
  p. 
  579, 
  pi. 
  XLVi, 
  fig. 
  

  

  3, 
  1879. 
  

   Yoldia 
  suhequilatera 
  Yerkill, 
  Traus. 
  Conn. 
  Acatl., 
  VI, 
  pp. 
  229, 
  279, 
  1884 
  (in 
  j^art) 
  ; 
  

  

  Expl. 
  Albatross, 
  Report 
  U. 
  S. 
  Com. 
  Fish 
  and 
  Fisheries 
  for 
  1883, 
  p. 
  576, 
  1885 
  

  

  (in 
  part). 
  

   Leda 
  suiequilatera 
  Dall, 
  Bull. 
  Mus. 
  Conip. 
  Zool., 
  XII, 
  p. 
  2.52, 
  1886. 
  

   Yoldia 
  )<ubcquilatera 
  Dall, 
  Bull. 
  U. 
  S. 
  Nat. 
  Mus., 
  No. 
  37, 
  p. 
  44, 
  1889. 
  

  

  Several 
  live 
  specimens 
  (No. 
  35204), 
  from 
  station 
  2037, 
  N. 
  lat. 
  38° 
  53', 
  

   W. 
  long. 
  69° 
  23' 
  30", 
  in 
  1,731 
  fathoms, 
  1883, 
  have 
  been 
  referred 
  to 
  this 
  

   species. 
  Although 
  younger 
  or 
  smaller 
  than 
  Jeffreys's 
  type, 
  they 
  agree 
  

   very 
  closely 
  with 
  his 
  figures 
  and 
  description. 
  The 
  shell 
  is 
  very 
  small, 
  

   very 
  thin 
  and 
  transparent, 
  polished, 
  lustrous, 
  but 
  scarcely 
  iridescent 
  

   and 
  marked 
  only 
  by 
  microscopic 
  lines 
  of 
  growth. 
  It 
  is 
  rather 
  com- 
  

   pressed, 
  nearly 
  elliptical 
  in 
  form, 
  with 
  the 
  beaks 
  prominent 
  above 
  the 
  

   dorsal 
  margin 
  and 
  turned 
  almost 
  directly 
  inward. 
  Both 
  ends 
  are 
  

   obtusely 
  rounded 
  and 
  nearly 
  equal 
  in 
  length, 
  so 
  that 
  it 
  is 
  impossible 
  to 
  

   determine 
  which 
  is 
  anterior 
  and 
  which 
  is 
  posterior 
  by 
  the 
  external 
  

   characters; 
  one 
  end, 
  supposed 
  to 
  be 
  the 
  anterior, 
  is 
  however 
  slightly 
  

   broader 
  than 
  the 
  other. 
  There 
  is 
  no 
  distinct 
  ligament 
  visible 
  externally. 
  

   The 
  hinge 
  plate 
  is 
  nearly 
  straight, 
  the 
  two 
  series 
  of 
  teeth 
  forming 
  but 
  a 
  

   slight 
  angle. 
  Interior 
  not 
  seen. 
  

  

  Our 
  specimens 
  measure 
  from 
  1.5 
  to 
  2.5 
  mm. 
  in 
  length. 
  South 
  to 
  

   Grenada, 
  in 
  92 
  fathoms. 
  — 
  Dall. 
  

  

  YOLDIELLA 
  EXPANSA 
  (Jeffreys). 
  

  

  (Plate 
  XCVII, 
  fig. 
  3.) 
  

  

  Leda 
  expansa 
  Jeffreys, 
  Ann. 
  Mag. 
  Nat. 
  Hist., 
  p. 
  431, 
  November, 
  1876; 
  Proe. 
  

  

  Zool. 
  Soc, 
  London, 
  p. 
  580, 
  pi. 
  xlvi, 
  fig. 
  4, 
  June, 
  1879. 
  

   Not 
  Yoldia 
  expansa 
  Verrill. 
  Trans. 
  Conn. 
  Acad., 
  YI, 
  p. 
  279, 
  1884. 
  

  

  Shell 
  oblong-ovate, 
  nearly 
  equilateral, 
  with 
  the 
  posterior 
  end 
  a 
  

   little 
  more 
  broadly 
  rounded 
  than 
  the 
  anterior; 
  both 
  regularly 
  obtuse. 
  

   Both 
  dorsal 
  margins 
  are 
  slightly 
  convex 
  and 
  slope 
  but 
  little. 
  The 
  

   hinge-plate 
  is 
  moderately 
  wide, 
  gently 
  arched, 
  with 
  sharp 
  dorsal 
  

   margins, 
  and 
  is 
  completely 
  interrupted 
  in 
  the 
  middle 
  by 
  a 
  deep, 
  

   angular 
  notch 
  for 
  the 
  resilium 
  which 
  is 
  rather 
  large 
  and 
  dark 
  and 
  is 
  

   attached 
  to 
  the 
  inner 
  surface 
  of 
  the 
  shell 
  below 
  the 
  beak. 
  In 
  the 
  right 
  

   valve, 
  there 
  are 
  ninei)osteriorteeth,includingoneor 
  two 
  very 
  small 
  i)rox- 
  

   imal 
  ones, 
  separated 
  from 
  the 
  margin 
  by 
  a 
  rather 
  wide, 
  smooth 
  space; 
  

   those 
  in 
  the 
  middle 
  of 
  the 
  series 
  are 
  long, 
  with 
  tapered, 
  acute 
  tips 
  which 
  

   are 
  bent 
  upward 
  and 
  toward 
  tlie 
  beaks, 
  and 
  at 
  base 
  are 
  V-shaped. 
  

   In 
  the 
  anterior 
  series, 
  which 
  is 
  a 
  little 
  the 
  longer, 
  there 
  are 
  ten 
  teeth, 
  

   including 
  two 
  or 
  three 
  very 
  small, 
  proximal 
  ones; 
  the 
  larger 
  ones 
  are 
  

   nearly 
  erect 
  with 
  the 
  tips 
  less 
  inclined 
  than 
  those 
  in 
  the 
  posterior 
  series; 
  

   they 
  are 
  separated 
  from 
  the 
  nnirgin 
  by 
  a 
  plain 
  space 
  about 
  as 
  wide 
  as 
  

  

  