﻿NO.U39. 
  DEEP-WATEB 
  MOLLUSCA—VEBRILL 
  AND 
  BUSS. 
  873 
  

  

  rior 
  acute, 
  curved, 
  V-shaped 
  teeth; 
  at 
  the 
  proximal 
  end 
  of 
  the 
  posterior 
  

   series, 
  iu 
  the 
  left 
  valve, 
  there 
  is 
  an 
  oblong, 
  prominent, 
  tooth-like 
  process, 
  

   much 
  larger 
  than 
  the 
  adjacent 
  teeth. 
  Three 
  or 
  four 
  of 
  the 
  distal 
  teeth, 
  

   on 
  each 
  side, 
  are 
  decidedly 
  large, 
  prominent 
  and 
  acute 
  with 
  the 
  tip 
  

   curved 
  outward, 
  but 
  the 
  size 
  decreases 
  regularly 
  toward 
  the 
  center. 
  

   There 
  is 
  a 
  well 
  developed 
  dark 
  ligament, 
  visible 
  externally, 
  both 
  before 
  

   and 
  behind 
  the 
  beaks. 
  The 
  surface 
  is 
  covered 
  by 
  relatively 
  rather 
  

   large, 
  distant, 
  concentric 
  ridges 
  and 
  furrows, 
  easily 
  visible 
  under 
  a 
  lens, 
  

   which 
  are 
  everywhere 
  covered 
  by 
  very 
  regular 
  microscopic 
  lines 
  and 
  

   grooves 
  of 
  about 
  equal 
  width. 
  

  

  Length 
  of 
  the 
  largest 
  valve, 
  4.25 
  mm. 
  ; 
  height, 
  2.8 
  mm. 
  

  

  A 
  few 
  specimens, 
  at 
  four 
  stations, 
  between 
  IST. 
  lat. 
  39° 
  49', 
  W. 
  long. 
  08° 
  

   28' 
  30", 
  and 
  N. 
  lat. 
  36° 
  47', 
  W. 
  long. 
  73° 
  9' 
  30", 
  iu 
  1,451 
  to 
  1,685 
  fathoms, 
  

   1883-1886. 
  

  

  This 
  species 
  is 
  remarkable 
  for 
  its 
  oblong-ovate 
  form 
  and 
  very 
  regular 
  

   concentric 
  sculpture, 
  consisting 
  of 
  fine 
  ridges 
  and 
  furrows 
  which 
  are 
  in 
  

   turn 
  everywhere 
  covered 
  with 
  regular 
  microscopic 
  lines. 
  This 
  species 
  

   was 
  at 
  iirst 
  thought 
  to 
  be 
  1'. 
  expansa 
  (Jeffreys) 
  which 
  it 
  resembles 
  in 
  

   form, 
  but 
  additional 
  specimens 
  and 
  more 
  careful 
  study 
  show 
  that 
  the 
  

   species 
  are 
  very 
  distinct. 
  In 
  1'. 
  expansa 
  the 
  hinge-margin 
  is 
  much 
  

   straighter, 
  the 
  teeth 
  fewer 
  and 
  different 
  iu 
  form, 
  the 
  resilial 
  pit 
  very 
  

   different, 
  the 
  two 
  ends 
  of 
  the 
  shell 
  more 
  nearly 
  equal, 
  and 
  the 
  sculp- 
  

   ture 
  quite 
  different. 
  

  

  Our 
  species 
  differs 
  considerably 
  from 
  the 
  typical 
  forms 
  of 
  Yoldiella 
  

   in 
  having 
  a 
  more 
  oblong 
  form 
  with 
  both 
  ends 
  evenly 
  rounded, 
  a 
  well- 
  

   developed 
  ligament, 
  and 
  a 
  more 
  evident 
  resilial 
  fossette 
  or 
  chondro- 
  

   phore 
  which, 
  however, 
  is 
  situated 
  decidedly 
  below 
  the 
  hinge-plate. 
  

   The 
  existence 
  of 
  a 
  peculiar 
  tooth-like 
  process 
  adjacent 
  to 
  the 
  resilial 
  

   notch 
  would 
  be 
  a 
  character 
  of 
  considerable 
  importance 
  were 
  it 
  con- 
  

   stant, 
  but 
  the 
  specimens 
  show 
  great 
  variation 
  in 
  its 
  development; 
  in 
  

   some, 
  it 
  is 
  even 
  almost 
  abortive. 
  These 
  distinctive 
  characters, 
  although 
  

   important, 
  seem 
  hardly 
  worthy 
  of 
  generic 
  distinction. 
  

  

  Subfaixiily 
  IM^LLETIN"^. 
  

  

  MALLETIA 
  Desnioulins, 
  1832 
  (restricted). 
  

  

  Malletia 
  Verrill 
  aud 
  Bush, 
  Amer. 
  Journ. 
  Sci., 
  Ill, 
  pp. 
  56, 
  63, 
  January, 
  1897. 
  

  

  Type. 
  — 
  MaUetia 
  chilensis 
  Desmoulins. 
  

  

  We 
  have 
  restricted 
  this 
  grouj) 
  to 
  those 
  species 
  having 
  a 
  nearly 
  

   smooth, 
  somewhat 
  compressed, 
  oblong 
  or 
  elliptical 
  shell, 
  blunt 
  pos- 
  

   teriorly, 
  without 
  any 
  definite 
  rostrum 
  or 
  carination. 
  The 
  carinated 
  

   aud 
  rostrated 
  species 
  that 
  have 
  been 
  i)laced 
  in 
  it 
  will 
  thus 
  be 
  referred 
  

   to 
  ISfeilo 
  H. 
  and 
  A. 
  Adams. 
  The 
  resilium 
  is 
  wanting, 
  or 
  else 
  represented 
  

   by 
  a 
  special 
  part 
  of 
  the 
  ligament, 
  external 
  to 
  the 
  teeth. 
  The 
  ligament 
  

   is 
  well 
  developed 
  and 
  prominent. 
  The 
  sii^hon 
  tubes 
  are 
  long 
  and 
  

   united 
  nearly 
  to 
  the 
  tips. 
  

  

  