﻿862 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  vol.xx. 
  

  

  Yoldia 
  ohesa 
  Verrill, 
  Amer. 
  Joum. 
  Sci., 
  VII, 
  pp. 
  46, 
  412, 
  503, 
  1874. 
  — 
  Smith 
  and 
  

   HAR(iER, 
  Trans. 
  Conn. 
  Acad., 
  Ill, 
  pp. 
  18, 
  23, 
  1874. 
  — 
  Verrill, 
  Explorations 
  

   Casco 
  Bay, 
  itp. 
  352, 
  368, 
  1874 
  ; 
  Inveit. 
  Auira. 
  Vineyard 
  Sd., 
  p. 
  396, 
  1874. 
  

  

  Portlandia 
  lueida 
  G. 
  O. 
  Sars, 
  MoUusca 
  lleg. 
  Arcticte 
  Norvegitc, 
  p. 
  37, 
  pi. 
  4, 
  figs. 
  

   8a, 
  Sb, 
  1878. 
  

  

  Lcdd 
  lueida 
  .Jeffreys, 
  Proc. 
  Zool. 
  Soc, 
  London, 
  p. 
  578, 
  1879. 
  

  

  Yoldia 
  lueida 
  Verrill, 
  Trans. 
  Conn. 
  Acad., 
  V, 
  pi. 
  Xliv, 
  fig. 
  1, 
  1882; 
  vi, 
  p. 
  279, 
  1884 
  

   (in 
  part); 
  Expl. 
  Alhatrofis, 
  Report 
  U. 
  S. 
  Com. 
  Fish 
  and 
  Fislieries 
  for 
  1883, 
  

   p. 
  576, 
  1885 
  (in 
  part).— 
  Bush, 
  Bull. 
  Mus.Comp. 
  Zoo.l, 
  XXIII, 
  p. 
  233, 
  1893. 
  

  

  Yoldiella 
  lueida 
  Verrill 
  and 
  Bush, 
  Amer. 
  Journ. 
  Sci., 
  Ill, 
  p. 
  55, 
  fig. 
  14, 
  January, 
  

   1897. 
  

  

  Shell 
  small, 
  swollen, 
  subovate, 
  with 
  a 
  posterior 
  angle, 
  smooth, 
  or 
  

   more 
  or 
  less 
  striolate, 
  iridescent. 
  The 
  umbos 
  are 
  but 
  little 
  prominent, 
  

   in 
  front 
  of 
  the 
  middle; 
  the 
  beaks 
  interrujjted 
  or 
  obliterated 
  by 
  the 
  dark 
  

   central 
  cartilage 
  which 
  occupies 
  a 
  relatively 
  large 
  notch 
  intersecting 
  

   the 
  entire 
  thickness 
  of 
  the 
  hinge-margin. 
  The 
  antero-dorsal 
  margin 
  is 
  

   convex 
  with 
  the 
  edge 
  a 
  little 
  expanded; 
  it 
  slopes 
  rapidly 
  from 
  the 
  

   beak 
  to 
  the 
  anterior 
  end 
  which 
  is 
  obtusely 
  rounded; 
  the 
  ventral 
  mar- 
  

   gin 
  is 
  broadly 
  and 
  regularly 
  curved 
  nearly 
  to 
  the 
  posterior 
  end 
  where 
  

   there 
  is 
  a 
  slight 
  protrusion 
  corresponding 
  to 
  a 
  faint 
  undulation 
  of 
  the 
  

   surface; 
  the 
  posterior 
  end 
  is 
  somewhat 
  wedge-shaped, 
  a 
  little 
  com- 
  

   pressed 
  and 
  tapered, 
  and 
  makes 
  a 
  distinct 
  but 
  obtuse 
  angle 
  where 
  it 
  

   joins 
  the 
  dorsal 
  margin 
  in 
  line 
  with 
  a 
  rounded 
  posterior 
  ridge 
  running 
  

   from 
  the 
  convex 
  part 
  of 
  the 
  umbos; 
  just 
  below 
  the 
  angle 
  the 
  margin 
  is 
  

   usually 
  convex 
  or 
  subtruncate 
  and 
  without 
  any 
  definite 
  lower 
  angle; 
  

   the 
  posterior 
  dorsal 
  margin 
  slopes 
  less 
  rapidly 
  than 
  the 
  anterior, 
  is 
  

   nearly 
  straight 
  with 
  the 
  edge 
  comi^ressed 
  and 
  a 
  little 
  expanded 
  into 
  a 
  

   thin 
  keel 
  which 
  is 
  usually 
  slightly 
  convex 
  in 
  the 
  middle. 
  The 
  hinge- 
  

   margin 
  is 
  strong, 
  somewhat 
  prolonged, 
  scarcely 
  angulated 
  in 
  the 
  middle; 
  

   the 
  part 
  in 
  front 
  of 
  the 
  chondrophore 
  is 
  well-arched 
  and 
  bears, 
  in 
  the 
  

   largest 
  specimens, 
  nine 
  or 
  ten, 
  sharp, 
  prominent, 
  angular 
  teeth, 
  of 
  which 
  

   two 
  or 
  three 
  nearest 
  the 
  beak 
  are 
  quite 
  small; 
  the 
  posterior 
  i)ortion 
  is 
  

   nearly 
  straight, 
  a 
  little 
  longer 
  and 
  narrower 
  than 
  the 
  anterior 
  and 
  bears 
  

   about 
  eleven 
  thin, 
  sharp, 
  erect 
  teeth, 
  counting 
  one 
  or 
  two 
  minute 
  proxi- 
  

   mal 
  ones; 
  a 
  thin 
  smooth 
  margin 
  extends 
  outside 
  both 
  series 
  of 
  teeth. 
  

   The 
  cartilage-pit 
  is 
  relatively 
  large, 
  in 
  the 
  form 
  of 
  a 
  notch, 
  and 
  cuts 
  

   through 
  the 
  hinge-margin 
  into 
  the 
  substance 
  of 
  the 
  beak 
  itself; 
  it 
  is 
  

   occupied 
  by 
  a 
  dark 
  brown 
  resiliuin 
  which 
  usually 
  shows 
  plainly 
  exter- 
  

   nally. 
  Just 
  in 
  front 
  of 
  the 
  cartilage-pit 
  on 
  its 
  border 
  within 
  the 
  series 
  

   of 
  teeth, 
  there 
  is 
  a 
  small 
  conical, 
  tooth 
  like 
  process 
  in 
  both 
  valves. 
  The 
  

   ligament 
  is 
  thin 
  and 
  delicate. 
  Externally 
  the 
  shell 
  is 
  covered 
  with 
  a 
  

   glossy, 
  yellowish, 
  or 
  j)ale 
  olive 
  epidermis 
  which 
  reflects 
  brilliant 
  pris- 
  

   matic 
  colors; 
  the 
  surface 
  is 
  marked 
  by 
  faint 
  lines 
  of 
  growth 
  and 
  fre- 
  

   quently 
  also 
  with 
  fine 
  concentric 
  grooves 
  or 
  sulci, 
  especially 
  toward 
  

   the 
  ventral 
  and 
  anterior 
  margins; 
  in 
  many 
  specimens 
  these 
  are 
  absent. 
  

  

  Length 
  of 
  one 
  of 
  the 
  largest 
  specimens, 
  7 
  mm.; 
  height, 
  4.25 
  mm.; 
  

   breadth, 
  3.2 
  mm. 
  

  

  Found 
  in 
  small 
  numbers, 
  at 
  many 
  stations, 
  between 
  N. 
  lat. 
  43° 
  39', 
  

  

  