﻿104 
  

  

  COLLECTIONS 
  PKOM 
  MELAITESIA. 
  

  

  in 
  form, 
  the 
  more 
  usual 
  outline 
  being 
  represented 
  by 
  Reeve's 
  fig. 
  

   47 
  h, 
  which 
  he 
  wrongly 
  ascribes 
  to 
  the 
  West-Indian 
  species. 
  The 
  

   difference 
  in 
  the 
  angle 
  of 
  divarication 
  of 
  the 
  ridges 
  is 
  at 
  once 
  seen 
  

   by 
  comparing 
  the 
  two 
  figures 
  47a 
  and 
  47 
  h. 
  

  

  43. 
  Diplodonta 
  subcrassa. 
  (Plate 
  VII. 
  figs. 
  I, 
  II.) 
  

  

  Shell 
  roundly 
  subquadrangular, 
  only 
  moderately 
  inflated, 
  thickish, 
  

   decidedly 
  inequilateral, 
  dirty 
  white, 
  not 
  glossy. 
  Anterior 
  side 
  

   shorter 
  than 
  the 
  posterior, 
  somewhat 
  pointed 
  at 
  the 
  extremity 
  ; 
  

   hinder 
  side 
  very 
  broad, 
  squarish, 
  yet 
  rounded. 
  Posterior 
  dorsal 
  

   margin 
  straightish, 
  only 
  a 
  trifle 
  oblique 
  ; 
  anterior 
  a 
  little 
  concave 
  

   near 
  the 
  beaks, 
  then 
  feebly 
  curved 
  and 
  suddenly 
  descending. 
  

   Ventral 
  outline 
  arcuate, 
  considerably 
  upcurving 
  in 
  front. 
  Surface 
  

   concentrically 
  finely 
  striated, 
  somewhat 
  uneven 
  through 
  periodic 
  

   interruptions 
  of 
  growth. 
  Umbones 
  small, 
  contiguous, 
  incurved, 
  

   pellucid, 
  located 
  in 
  advance 
  of 
  the 
  median 
  line. 
  Hinge-teeth 
  

   rather 
  strong, 
  posterior 
  of 
  the 
  right 
  valve 
  and 
  anterior 
  in 
  the 
  

   left 
  stout, 
  subequal, 
  bifid, 
  and 
  the 
  anterior 
  in 
  the 
  former 
  is 
  rather 
  

   thicker 
  than 
  the 
  hinder 
  in 
  the 
  latter, 
  which 
  is 
  sublamellar. 
  Muscular 
  

   scars 
  somewhat 
  small, 
  deepish, 
  subequal. 
  Interior 
  of 
  the 
  valves 
  

   not 
  very 
  glossy, 
  roughish. 
  

  

  Length 
  15 
  millim., 
  height 
  14, 
  diameter 
  8|. 
  

  

  Hab. 
  West 
  Island, 
  Prince 
  of 
  Wales 
  Channel, 
  Torres 
  Straits, 
  7 
  fms. 
  

  

  This 
  is 
  rather 
  a 
  solid 
  species 
  and 
  peculiarly 
  acuminated 
  at 
  the 
  

   extremity 
  in 
  front, 
  with 
  rather 
  conspicuous 
  lines 
  indicating 
  periodic 
  

   growth. 
  

  

  44. 
  Diplodonta 
  sublateralis. 
  (Plate 
  VII. 
  fig. 
  K.) 
  

  

  Shell 
  very 
  inequilateral, 
  much 
  broader 
  behind 
  than 
  in 
  front, 
  

   scarcely 
  longer 
  than 
  high, 
  moderately 
  infiated, 
  white, 
  finely 
  concen- 
  

   trically 
  sculptured 
  with 
  the 
  lines 
  of 
  growth. 
  Posterior 
  dorsal 
  

   margin 
  nearly 
  horizontal, 
  straight 
  at 
  first, 
  then 
  gradually 
  curving 
  

   into 
  the 
  broadly 
  arcuate 
  lateral 
  outline. 
  Front 
  dorsal 
  edge 
  some- 
  

   what 
  oblique, 
  scarcely 
  recurved 
  near 
  the 
  beak, 
  but 
  afterwards 
  

   rounding 
  into 
  the 
  side 
  margin, 
  which 
  is 
  very 
  mu.ch 
  more 
  suddenly 
  

   curvate 
  than 
  at 
  the 
  opposite 
  end. 
  Ventral 
  margin 
  more 
  sharply 
  

   arched 
  than 
  the 
  posterior, 
  but 
  less 
  so 
  than 
  the 
  anterior. 
  Umbones 
  

   small, 
  acute, 
  only 
  slightly 
  elevated, 
  situated 
  far 
  in 
  advance 
  of 
  the 
  

   centre. 
  Hinge-plate 
  narrow 
  in 
  the 
  right 
  valve, 
  conspicuously 
  

   grooved 
  in 
  front 
  of 
  the 
  two 
  cardinal 
  teeth 
  ; 
  of 
  these 
  the 
  anterior 
  is 
  

   very 
  small, 
  lamellar, 
  and 
  falls 
  perpendicularly 
  beneath 
  the 
  beak, 
  

   the 
  posterior 
  being 
  about 
  three 
  times 
  as 
  thick 
  and 
  deeply 
  bisected. 
  

   The 
  ligamental 
  furrow 
  is 
  narrow 
  and 
  5| 
  millim. 
  in 
  length. 
  The 
  

   muscular 
  scars 
  are 
  subequal, 
  the 
  posterior 
  a 
  trifle 
  broader. 
  Length 
  

   19| 
  millim., 
  beight 
  18|^, 
  diameter 
  10. 
  

  

  Hah. 
  Torres 
  Straits, 
  7-10 
  fms. 
  

  

  Only 
  a 
  right 
  valve 
  of 
  this 
  species 
  was 
  obtained 
  by 
  Dr. 
  Coppinger, 
  

   which, 
  however, 
  is 
  apparently 
  distinct 
  in 
  form, 
  the 
  chief 
  distin- 
  

  

  