﻿780 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  

  

  A 
  few 
  separate 
  valves, 
  off 
  Cape 
  Hatteras, 
  North 
  Carolina, 
  iu 
  10 
  to 
  17 
  

   fathoms, 
  1884. 
  

  

  MONTACUTA 
  BIDENTATA 
  (Montagu), 
  variety 
  FRAGIUS, 
  new. 
  

   (Plate 
  XCII, 
  fig. 
  8.) 
  

  

  Shell 
  siibellii)tical, 
  inequilateral, 
  both 
  ends 
  broadly 
  rounded, 
  thin, 
  

   fragile, 
  covered 
  with 
  delicate 
  lines 
  of 
  growth. 
  The 
  umbos 
  are 
  flat- 
  

   tened; 
  beaks 
  but 
  slightly 
  prominent. 
  The 
  teeth 
  in 
  the 
  right 
  valve 
  are 
  

   smaller 
  and 
  more 
  delicate 
  than 
  in 
  the 
  typical 
  bidentata, 
  and 
  diverge 
  

   but 
  slightly 
  from 
  the 
  dorsal 
  margin, 
  as 
  in 
  that 
  species. 
  

  

  Length, 
  4 
  mm.; 
  height, 
  3 
  mm. 
  

  

  One 
  specimen 
  (No. 
  40134), 
  station 
  810-17, 
  in 
  Narragansett 
  Bay, 
  in 
  

   8i 
  to 
  10 
  fathoms, 
  1880. 
  

  

  MONTACUTA 
  STRIATULA, 
  new 
  species. 
  

   (Plate 
  XCIII, 
  fig. 
  9.) 
  

  

  Shell 
  rather 
  large, 
  thin 
  and 
  somewhat 
  hyaline, 
  compressed, 
  broad- 
  

   elliptical 
  with 
  both 
  ends 
  well 
  rounded, 
  the 
  anterior 
  much 
  the 
  longer. 
  

   Antero-dorsal 
  margin 
  nearly 
  straight 
  with 
  a 
  gradnal 
  slope; 
  anterior 
  

   end 
  broadly 
  and 
  regularly 
  rounded, 
  its 
  outline 
  forming 
  nearly 
  the 
  seg- 
  

   ment 
  of 
  a 
  circle; 
  ventral 
  margin 
  broadly 
  and 
  evenly 
  convex; 
  posterior 
  

   end 
  bluntly 
  rounded 
  with 
  its 
  dorsal 
  jnargin 
  slightly 
  concave 
  and 
  slop 
  

   ing 
  rapidly. 
  Umbos 
  Jiot 
  swollen; 
  beaks 
  acute 
  and 
  only 
  a 
  little 
  promi- 
  

   nent. 
  Surface 
  covered 
  with 
  fine, 
  regular, 
  concentric, 
  microscopic 
  stri<e 
  

   and 
  more 
  distant 
  lines 
  of 
  growth. 
  Interior 
  somewhat 
  shining 
  with 
  

   inconspicuous 
  muscular 
  scars. 
  Hinge-margin 
  thin, 
  delicate, 
  only 
  

   slightly 
  thickened. 
  In 
  the 
  right 
  valve 
  there 
  is, 
  on 
  each 
  side 
  of 
  the 
  

   beaks, 
  a 
  short, 
  rather 
  delicate, 
  elevated, 
  triangular 
  tooth, 
  terminating 
  

   distally 
  with 
  an 
  abrupt 
  slope; 
  these 
  are 
  nearly 
  equal 
  in 
  size 
  and 
  length, 
  

   the 
  anterior 
  one 
  being 
  slightly 
  the 
  shorter 
  and 
  more 
  angular. 
  They 
  are 
  

   separated 
  by 
  a 
  V-shaped 
  notch, 
  the 
  sides 
  of 
  which 
  form 
  nearly 
  a 
  right 
  

   angle. 
  In 
  the 
  left 
  valve 
  there 
  are 
  two 
  thin, 
  slightly 
  prominent 
  eleva- 
  

   tions, 
  scarcely 
  worthy 
  the 
  name 
  of 
  teeth, 
  separated 
  by 
  a 
  very 
  wide 
  

   angle 
  under 
  the 
  beak. 
  

  

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

  

  This 
  species 
  is 
  much 
  larger 
  than 
  any 
  of 
  our 
  other 
  species 
  of 
  this 
  

   genus, 
  and 
  may 
  possibly 
  prove 
  to 
  be 
  identical 
  with 
  M. 
  bowmani, 
  

   described 
  and 
  figured 
  by 
  Holmes.' 
  Owing, 
  however, 
  to 
  the 
  shortness 
  

   of 
  the 
  description 
  and 
  small 
  size 
  of 
  the 
  figures, 
  this 
  question 
  cannot 
  

   be 
  definitely 
  decided 
  without 
  a 
  careful 
  comparison 
  with 
  authentic 
  

   specimens. 
  

  

  A 
  few 
  separate 
  valves 
  were 
  found 
  oft" 
  Cape 
  Hatteras, 
  North 
  Caro- 
  

   lina, 
  in 
  15 
  to 
  48 
  fathoms, 
  1883-84. 
  

  

  1 
  Post-pleiocene 
  fossils 
  of 
  South 
  Carolina, 
  j>. 
  30, 
  pi. 
  vii, 
  fig. 
  2, 
  1860. 
  

  

  