﻿340 
  CONTRIBUTIONS 
  TO 
  THE 
  GEOLOGY 
  OF 
  

  

  the 
  posterior 
  end, 
  in 
  the 
  ribs, 
  and 
  in 
  the 
  less 
  distinctness 
  of 
  the 
  trans- 
  

   verse 
  striae. 
  

  

  Nucula 
  parva. 
  

  

  41. 
  Shell 
  ovate, 
  inflated, 
  rounded 
  before, 
  not 
  much 
  produced, 
  but 
  

   rapidly 
  tapering 
  to 
  a 
  truncated 
  point 
  behind, 
  furnished 
  with 
  about 
  

   twelve 
  rather 
  coarse 
  concentric 
  folds 
  or 
  ridges, 
  and 
  a 
  longitudinal 
  

   gently 
  depressed 
  groove 
  or 
  undulation 
  of 
  surface, 
  running 
  from 
  near 
  

   the 
  beak 
  to 
  the 
  posterior 
  basal 
  margin 
  ; 
  beaks 
  nearly 
  central 
  ; 
  anterior 
  

   series 
  of 
  teeth 
  slightly 
  arched 
  ; 
  posterior 
  series 
  nearly 
  straight 
  ; 
  margin 
  

   entire 
  ; 
  cavity 
  rather 
  deep. 
  Length, 
  three-twentieths 
  ; 
  height, 
  two- 
  

   twentieths 
  of 
  an 
  inch. 
  

  

  Locality, 
  same 
  as 
  the 
  preceding. 
  

  

  Ostrea 
  sinuosa. 
  

  

  42. 
  Shell 
  sub-orbicular, 
  or 
  equilaterally 
  sub-triangular; 
  inferior 
  

   valve 
  moderately 
  convex, 
  with 
  the 
  laminae 
  of 
  growth 
  profoundly 
  pli- 
  

   cated 
  into 
  loops, 
  which 
  are" 
  imbricated 
  so 
  as 
  to 
  produce 
  regularly 
  radi- 
  

   ating 
  ribs 
  ; 
  hinge-plane 
  depressed, 
  and 
  in 
  a 
  line 
  with 
  the 
  dorsal 
  margin, 
  

   which 
  is 
  long 
  and 
  straight, 
  the 
  sides 
  of 
  the 
  inferior 
  valve 
  being 
  dilated 
  

   into 
  the 
  form 
  of 
  ears 
  ; 
  fosset 
  placed 
  symmetrically 
  and 
  centrally 
  in 
  the 
  

   hinge, 
  and 
  less 
  than 
  one-third 
  its 
  length, 
  and 
  curving 
  suddenly 
  at 
  its 
  

   termination 
  in 
  a 
  narrow 
  groove 
  ; 
  beak 
  slightly 
  curved 
  to 
  the 
  right 
  

   and 
  truncate 
  ; 
  muscular 
  impression 
  small 
  ; 
  inferior 
  valve 
  very 
  slightly 
  

   convex 
  or 
  flat, 
  nearly 
  circular, 
  with 
  concentric 
  almost 
  circular 
  wrinkles. 
  

   Length 
  of 
  the 
  specimen 
  four 
  and 
  a 
  half 
  inches 
  ; 
  diameter 
  between 
  the 
  

   ears 
  five 
  and 
  a 
  half 
  inches 
  ; 
  diameter 
  of 
  flat 
  valve 
  four 
  inches. 
  

  

  Locality, 
  Evergreen, 
  James 
  river, 
  in 
  the 
  lower 
  or 
  green 
  sand 
  stratum 
  

   of 
  the 
  Eocene. 
  This 
  very 
  beautiful 
  fossil 
  oyster 
  will 
  be 
  seen 
  to 
  differ 
  

   from 
  the 
  O. 
  compressirostra 
  in 
  several 
  essential 
  particulars, 
  especially 
  

   in 
  the 
  structure 
  of 
  the 
  hinge, 
  in 
  the 
  more 
  symmetrical 
  and 
  profound 
  

   plications 
  on 
  the 
  inferior 
  valve, 
  in 
  its 
  less 
  convexity, 
  and 
  in 
  its 
  more 
  

   regular 
  dilatation 
  on 
  the 
  upper 
  margin 
  into 
  partial 
  ears. 
  

  

  Cytherea 
  ovata. 
  

  

  43. 
  Shell 
  subovate, 
  somewhat 
  inflated, 
  with 
  concentric 
  transverse 
  

  

  