﻿870 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  vol.xx. 
  

  

  The 
  pallial 
  sinus 
  is 
  rather 
  wide 
  and 
  moderately 
  deep, 
  but 
  is 
  invisible 
  

   in 
  most 
  specimens. 
  

  

  Length 
  of 
  the 
  largest 
  specimen, 
  3.0 
  ram.; 
  height, 
  2.3 
  mm. 
  

  

  A 
  number 
  of 
  specimens, 
  at 
  about 
  fifteen 
  stations, 
  between 
  jST. 
  lat. 
  

   42° 
  33', 
  W. 
  long. 
  09° 
  58.5', 
  and 
  54^. 
  lat. 
  35° 
  12' 
  10", 
  W. 
  long. 
  74° 
  57' 
  15", 
  

   in 
  100 
  to 
  705 
  fathoms, 
  1878-188G. 
  

  

  This 
  species 
  is 
  distinguished 
  from 
  YoldieUa 
  frigida, 
  and 
  most 
  of 
  the 
  

   other 
  small 
  species 
  which 
  it 
  resembles, 
  by 
  its 
  narrower, 
  or 
  lower, 
  and 
  

   more 
  compressed 
  form, 
  more 
  delicate 
  shell, 
  straighter 
  dorsal 
  margin, 
  

   and 
  the 
  more 
  central 
  prolongation 
  of 
  the 
  i^osterior 
  end. 
  It 
  is 
  appar- 
  

   ently 
  more 
  nearly 
  related 
  to 
  the 
  smaller 
  species, 
  Y. 
  minuscula, 
  than 
  

   to 
  any 
  other. 
  The 
  latter 
  has 
  a 
  smaller, 
  shorter, 
  and 
  more 
  swollen 
  

   shell, 
  more 
  convex 
  ventrally, 
  with 
  the 
  hinge-margin 
  somewhat 
  more 
  

   ungulated. 
  

  

  YOLDIELLA 
  MINUSCULA, 
  new 
  species. 
  

  

  (Plate 
  LXXIX, 
  figs. 
  2,7.) 
  

  

  Toldia 
  jeffreysi 
  Verrill, 
  Trans. 
  Conn. 
  Acad., 
  VI, 
  pp. 
  229, 
  279, 
  1884; 
  Expl, 
  

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

  

  Shell 
  minute, 
  broad-ovate, 
  covered 
  with 
  microscopic, 
  pretty 
  regular 
  

   concentric 
  striations, 
  with 
  a 
  very 
  lustrous, 
  somewhat 
  iridescent, 
  yel- 
  

   lowish 
  epidermis. 
  The 
  two 
  ends 
  are 
  nearly 
  equal 
  in 
  length; 
  the 
  

   posterior 
  somewhat 
  narrowed 
  and 
  obtuse 
  at 
  the 
  end, 
  the 
  anterior 
  well- 
  

   rounded. 
  The 
  umbos 
  are 
  not 
  prominent 
  and 
  the 
  beaks 
  are 
  very 
  small 
  

   and 
  project 
  but 
  slightly 
  above 
  the 
  margin. 
  The 
  anterodorsal 
  margin 
  is 
  

   slightly 
  convex 
  at 
  first, 
  and 
  nearly 
  horizontal, 
  and 
  passes 
  gradually 
  

   into 
  the 
  curve 
  of 
  the 
  anterior 
  end; 
  ventral 
  margin 
  is 
  broad 
  and 
  nearly 
  

   uniformly 
  convex 
  ; 
  the 
  i)osterior 
  end 
  is 
  a 
  little 
  produced 
  in 
  the 
  middle 
  

   and 
  forms 
  there 
  a 
  slight 
  obtuse 
  angle; 
  the 
  postero-dorsal 
  margin 
  is 
  a 
  

   little 
  convex 
  and 
  nearly 
  horizontal 
  at 
  first 
  and 
  then 
  slopes 
  rather 
  

   rapidly 
  to 
  the 
  tip. 
  The 
  hinge-margin 
  is 
  thin 
  and 
  delicate; 
  the 
  two 
  

   series 
  of 
  teeth 
  lie 
  nearly 
  in 
  a 
  straight 
  line 
  but 
  the 
  anterior 
  one 
  is 
  a 
  

   little 
  obliipie, 
  so 
  that 
  they 
  form 
  a 
  very 
  wide 
  angle 
  at 
  the 
  beaks 
  where 
  

   the 
  resilium 
  entirely 
  interrupts 
  the 
  hinge-margin 
  forming 
  a 
  wide 
  notch 
  

   without 
  any 
  definite 
  pit 
  or 
  shelf; 
  the 
  teeth 
  are 
  small, 
  very 
  oblique, 
  and 
  

   only 
  slightly 
  prominent; 
  there 
  are 
  only 
  about 
  five 
  in 
  the 
  anterior 
  and 
  

   six 
  in 
  the 
  posterior 
  series. 
  

  

  Length, 
  about 
  2.3 
  mm.; 
  height, 
  about 
  1.5 
  mm. 
  

  

  Only 
  a 
  few 
  sj^ecimens, 
  at 
  four 
  stations, 
  between 
  K. 
  lat 
  41° 
  53', 
  W. 
  

   long. 
  65° 
  35', 
  and 
  N. 
  lat. 
  38° 
  27', 
  W. 
  long. 
  73° 
  2', 
  in 
  705 
  to 
  1,290 
  

   fathoms, 
  1883-1885. 
  

  

  This 
  very 
  minute 
  species 
  may, 
  with 
  a 
  larger 
  series, 
  prove 
  to 
  be 
  the 
  

   young 
  of 
  some 
  of 
  the 
  preceding 
  species. 
  

  

  