﻿UEEr-WATER 
  MOLLUSC 
  A— 
  VEBBILL 
  AND 
  BUSH. 
  823 
  

  

  Length 
  of 
  the 
  largest 
  specimens, 
  13 
  mm.; 
  height, 
  10 
  mm.; 
  breadth, 
  

   8 
  mm. 
  

  

  Three 
  specimens 
  were 
  found 
  at 
  three 
  stations, 
  off 
  Marthas 
  Vineyard, 
  

   in 
  100 
  to 
  115 
  fathoms, 
  1880-81. 
  

  

  This 
  vspecies 
  resembles 
  P. 
  undulata 
  in 
  sculpture, 
  but 
  the 
  latter 
  is 
  

   narrower 
  and 
  longer 
  in 
  form, 
  and 
  has 
  a 
  more 
  decidedly 
  longer 
  rostrum 
  ; 
  

   its 
  chrondrophore 
  is 
  shorter 
  and 
  broader, 
  and 
  not 
  so 
  distinctly 
  spoon- 
  

   shaped 
  distally, 
  while 
  the 
  marginal 
  notch 
  in 
  front 
  of 
  it 
  is 
  relatively 
  

   much 
  snuiller. 
  

  

  PERIPLOMA 
  UNDULATA 
  Verrill. 
  

   (Plates 
  LXXIX, 
  lig. 
  1; 
  LXXXYII, 
  fig. 
  5.) 
  

  

  Periploma 
  undulata 
  Verrill, 
  Trans. 
  Conn. 
  Acad., 
  VI, 
  pp. 
  433, 
  448, 
  1885. 
  

  

  A 
  few 
  specimens 
  were 
  found 
  at 
  six 
  stations 
  between 
  N. 
  lat. 
  39° 
  9', 
  

   W. 
  long. 
  73° 
  3' 
  15", 
  and 
  N. 
  lat. 
  36° 
  42', 
  W. 
  long. 
  74° 
  30', 
  in 
  541 
  to 
  81G 
  

   fathoms, 
  1884-1887. 
  

  

  Family 
  LIMID^. 
  

  

  LIMATULA 
  REGULARIS, 
  new 
  species. 
  

  

  Shell 
  small, 
  thin, 
  nearly 
  equilateral, 
  much 
  higher 
  than 
  long, 
  with 
  

   the 
  hinge 
  line 
  straight 
  and 
  rather 
  long. 
  Umbos 
  and 
  median 
  part 
  of 
  

   the 
  shell 
  swollen. 
  Beaks 
  rather 
  prominent, 
  directly 
  incurved. 
  Liga- 
  

   mental 
  area 
  relatively 
  large, 
  elongated, 
  diamond-shaped, 
  with 
  the 
  

   pointed 
  end 
  extending 
  nearly 
  to 
  the 
  angles 
  of 
  the 
  hinge-margin, 
  with 
  

   a 
  central, 
  more 
  sunken, 
  short, 
  rhomboidal 
  iigament-pit 
  which, 
  on 
  a 
  

   separate 
  valve, 
  forms 
  nearly 
  an 
  equilateral 
  triangle. 
  The 
  anterior 
  and 
  

   posterior 
  ends 
  are 
  nearly 
  e(]ually 
  curved, 
  a 
  little 
  convex, 
  but 
  slightly 
  

   narrowed 
  where 
  they 
  join 
  the 
  hinge-margin 
  and 
  form 
  a 
  distinct 
  obtuse 
  

   angle; 
  on 
  one 
  side, 
  supposed 
  to 
  be 
  anterior, 
  below 
  the 
  angle 
  the 
  mar- 
  

   gin 
  is 
  slightly 
  incurved 
  for 
  a 
  short 
  distance, 
  making 
  this 
  angle 
  less 
  

   obtnse 
  than 
  the 
  other. 
  The 
  ventral 
  margin 
  is 
  nearly 
  evenly 
  rounded, 
  

   forming 
  nearly 
  the 
  segment 
  of 
  a 
  circle. 
  The 
  surface 
  is 
  covered 
  with 
  

   small, 
  elevated, 
  radial 
  ridges 
  separated 
  by 
  concave 
  grooves 
  of 
  greater 
  

   breadth; 
  in 
  the 
  middle 
  of 
  the 
  shell 
  between 
  ten 
  and 
  twelve 
  of 
  the 
  

   ridges 
  are 
  distinctly 
  higher 
  and 
  thicker; 
  on 
  each 
  side 
  their 
  size 
  dimin- 
  

   ishes 
  outwardly, 
  so 
  that 
  near 
  the 
  angles 
  of 
  the 
  hinge 
  they 
  become 
  

   nearly 
  or 
  quite 
  obsolete, 
  the 
  last 
  ones 
  being 
  mere 
  raised, 
  microscopic 
  

   threads; 
  in 
  some 
  cases 
  smaller 
  ones 
  alternate 
  with 
  the 
  hirger 
  ones, 
  so 
  

   that 
  the 
  total 
  number 
  can 
  not 
  be 
  definitely 
  determined, 
  but 
  fifty 
  or 
  

   more 
  can 
  often 
  be 
  counted. 
  There 
  is 
  often 
  no 
  very 
  evident 
  median 
  

   external 
  sulcus, 
  such 
  as 
  occurs 
  in 
  several 
  related 
  species, 
  but 
  the 
  two 
  

   or 
  three 
  central 
  radii 
  are 
  often, 
  but 
  not 
  always, 
  distinctly 
  larger 
  than 
  

   the 
  rest. 
  The 
  radii 
  are 
  crossed 
  by 
  very 
  fine 
  lines 
  of 
  growth 
  not 
  suffi- 
  

   ciently 
  strong 
  to 
  render 
  them 
  at 
  all 
  nodulose. 
  The 
  inner 
  margin 
  is 
  

  

  