﻿NO. 
  1139. 
  DEEP-WATER 
  MOLLUSC 
  A— 
  VEBBILL 
  AND 
  BUSH. 
  869 
  

  

  broadly 
  rounded 
  and 
  slightly 
  produced 
  in 
  the 
  middle; 
  it 
  Joins 
  the 
  curve 
  

   of 
  the 
  posterior 
  end 
  with 
  a 
  scarcely 
  perceptible 
  incurvature 
  in 
  some 
  

   specimens; 
  the 
  posterior 
  end 
  is 
  obtusely 
  rounded 
  and 
  situated 
  about 
  

   midheight 
  of 
  the 
  shell. 
  The 
  dorsal 
  edges 
  of 
  the 
  valve 
  are 
  thin 
  and 
  a 
  

   little 
  pinched 
  up, 
  but 
  there 
  is 
  no 
  distinct 
  lunule 
  and 
  only 
  a 
  very 
  nar- 
  

   row 
  ligamental 
  furrow. 
  The 
  epidermis 
  is 
  polished 
  and 
  somewhat 
  iri- 
  

   descent, 
  and 
  marked 
  with 
  fine, 
  somewhat 
  irregular 
  lines 
  of 
  growth, 
  in 
  

   some 
  places 
  showing 
  laint, 
  microscopic, 
  radial 
  striations. 
  Color 
  of 
  the 
  

   dead 
  valves, 
  brownish 
  yellow. 
  Hinge-plate 
  strong, 
  narrow 
  near 
  the 
  

   beak, 
  wide 
  distally, 
  strongly 
  angled, 
  with 
  the 
  outer 
  edge 
  naked 
  and 
  

   rather 
  broad, 
  especially 
  anteriorly. 
  Teeth 
  large 
  and 
  prominent 
  dis- 
  

   tally, 
  with 
  about 
  three 
  small 
  proximal 
  ones; 
  about 
  eight 
  in 
  the 
  ante- 
  

   rior 
  and 
  ten 
  in 
  the 
  posterior 
  series. 
  The 
  resilial 
  pit 
  is 
  a 
  distinct, 
  

   triangular 
  fossette, 
  or 
  chondrophore, 
  on 
  the 
  face 
  of 
  the 
  margin, 
  cover- 
  

   ing 
  its 
  whole 
  breadth, 
  and 
  bordered 
  internally 
  by 
  a 
  thickened 
  edge 
  

   which 
  causes 
  an 
  excurvature 
  of 
  the 
  margin. 
  There 
  is 
  a 
  distinct 
  mar- 
  

   ginal 
  external 
  ligament 
  and 
  furrow, 
  or 
  escutcheon. 
  

  

  Length, 
  4,G 
  mm.; 
  height, 
  4.8 
  mm. 
  

  

  Three 
  separate 
  valves, 
  among 
  Foraminifera, 
  at 
  station 
  2385, 
  i^. 
  lat. 
  

   28° 
  51', 
  W. 
  long. 
  d>S^ 
  18', 
  in 
  730 
  fathoms, 
  1885. 
  

  

  In 
  outline 
  this 
  species 
  resembles 
  Y. 
  curia, 
  but 
  differs 
  in 
  its 
  wider 
  and 
  

   stouter 
  hinge-plate, 
  more 
  numerous 
  and 
  more 
  highly 
  developed 
  teeth, 
  

   and 
  especially 
  in 
  the 
  form 
  and 
  structure 
  of 
  the 
  resilial 
  pit. 
  

  

  YOLDIELLA 
  INCONSPICUA, 
  new 
  species. 
  

   (Plate 
  LXXIX, 
  figs. 
  3, 
  5.) 
  

  

  Shell 
  small, 
  thin, 
  delicate, 
  compressed, 
  subovate; 
  posterior 
  end 
  a 
  lit- 
  

   tle 
  produced 
  and 
  narrowed 
  medially. 
  Surface 
  lustrous 
  and 
  iridescent. 
  

   Umbos 
  scarcely 
  prominent; 
  beaks 
  small, 
  projecting 
  but 
  little 
  above 
  the 
  

   dorsal 
  margin. 
  The 
  antero-dorsal 
  margin 
  is 
  slightly 
  convex 
  and 
  nearly 
  

   horizontal 
  at 
  first, 
  then 
  slopes 
  gradually 
  to 
  the 
  evenly 
  rounded 
  anterior 
  

   end; 
  ventral 
  margin 
  broadly 
  rounded, 
  sliglitly 
  swollen 
  posteriorly, 
  

   ascending 
  more 
  rapidly 
  to 
  the 
  narrow 
  and 
  bluntly 
  rounded 
  posterior 
  

   end; 
  postero-dorsal 
  margin 
  nearly 
  straight 
  toward 
  the 
  beak, 
  then 
  

   slightly 
  convex 
  and 
  sloping 
  very 
  gradually. 
  The 
  surface 
  is 
  covered 
  

   with 
  fine, 
  pretty 
  regular, 
  concentric 
  grooves 
  and 
  raised 
  lines, 
  visible 
  

   only 
  under 
  the 
  microscope. 
  Epidermis 
  thin, 
  shining, 
  iridescent, 
  green- 
  

   ish 
  yellow. 
  The 
  hinge-margin 
  is 
  thin 
  and 
  delicate, 
  nearly 
  straight; 
  the 
  

   two 
  series 
  of 
  teeth 
  form 
  a 
  very 
  obtuse 
  angle 
  at 
  the 
  beaks 
  and 
  are 
  

   interrupted, 
  for 
  a 
  considerable 
  space, 
  by 
  the 
  resilium 
  which 
  does 
  not 
  lie 
  

   in 
  a 
  distinct 
  pit. 
  The 
  ligament 
  shows 
  as 
  a 
  delicate, 
  continuous 
  mar- 
  

   ginal 
  line, 
  both 
  in 
  front 
  of 
  and 
  behind 
  the 
  beaks. 
  The 
  teeth 
  are 
  small, 
  

   oblique, 
  V-shaped. 
  In 
  the 
  anterior 
  series 
  there 
  are 
  about 
  six 
  distinct 
  

   ones 
  with 
  one 
  or 
  two 
  minute 
  proximal 
  ones; 
  in 
  the 
  iwsterior, 
  about 
  

   seven 
  distinct 
  ones 
  with 
  one 
  or 
  two 
  rudimentary 
  ones 
  near 
  the 
  beak. 
  

  

  