﻿THE 
  TERTIARY 
  FORMATIONS 
  OP 
  VIRGINIA. 
  333 
  

  

  advance 
  of 
  the 
  end 
  of 
  the 
  hinge 
  ; 
  basal 
  margin 
  contracted 
  opposite 
  the 
  

   middle 
  of 
  the 
  hinge, 
  and 
  deeply 
  crenate. 
  Length, 
  three 
  and 
  a 
  half 
  

   inches. 
  

  

  Locality, 
  Shell 
  banks, 
  Prince 
  George 
  county. 
  Miocene. 
  

  

  ' 
  r 
  : 
  . 
  Lucina 
  speciosa. 
  

  

  28: 
  Shell 
  sub-elliptical, 
  inequilateral, 
  inflated, 
  rather 
  thin, 
  with 
  

   equal 
  close-set 
  rather 
  elevated 
  longitudinal 
  ribs, 
  and 
  regular 
  very 
  close 
  

   concentric 
  striae 
  ; 
  lunule 
  small, 
  very 
  distinct, 
  and 
  ovate-lanceolate 
  ; 
  

   beaks 
  small, 
  pointed, 
  and 
  slightly 
  prominent 
  beyond 
  the 
  general 
  curve 
  

   of 
  the 
  margin, 
  placed 
  about 
  one-third 
  the 
  transverse 
  length 
  of 
  the 
  shell 
  

   from 
  the 
  anterior 
  end 
  ; 
  cardinal 
  teeth 
  small, 
  diverging 
  ; 
  lateral 
  teeth 
  

   equal, 
  distinct, 
  and 
  nearly 
  equidistant 
  from 
  the 
  anterior 
  cardinal 
  ; 
  hinge 
  

   margin 
  regularly 
  arcuated, 
  the 
  rest 
  of 
  the 
  margin, 
  especially 
  the 
  poste- 
  

   rior 
  side, 
  crenate 
  within 
  ; 
  posterior 
  muscular 
  impression 
  elongated 
  and 
  

   slightly 
  curved. 
  Diameter, 
  three-tenths; 
  length, 
  eleven-twentieths; 
  

   height, 
  nine-twentieths 
  of 
  an 
  inch. 
  

  

  This 
  very 
  beautiful 
  shell 
  occurs 
  in 
  nearly 
  all 
  the 
  localities 
  of 
  the 
  

   Miocene 
  in 
  the 
  James 
  river 
  region. 
  

  

  Venus 
  cortinaria. 
  

  

  29. 
  Shell 
  sub-cordate, 
  inflated, 
  with 
  very 
  regular 
  concentric, 
  closely 
  

   approximate, 
  and 
  very 
  prominent 
  imbricated 
  ridges, 
  which 
  incline 
  to- 
  

   wards 
  the 
  beak, 
  except 
  the 
  portion 
  opposite 
  the 
  anterior, 
  basal, 
  and 
  

   posterior 
  margins, 
  where 
  they 
  decline 
  outwards 
  towards 
  the 
  margin 
  ; 
  

   beaks 
  moderately 
  prominent, 
  about 
  twice 
  as 
  far 
  from 
  the 
  anterior 
  as 
  

   t4JLe 
  posterior 
  end; 
  two 
  anterior 
  cardinal 
  teeth, 
  closely 
  approximate 
  

   above, 
  second 
  one 
  of 
  the 
  left 
  valve 
  thick 
  and 
  sub-bifid 
  ; 
  lunule 
  wide, 
  

   cordate 
  ; 
  basal 
  margin 
  crenate 
  within 
  ; 
  posterior 
  margin 
  short, 
  straight, 
  

   and 
  especially 
  at 
  the 
  lunule 
  finely 
  crenate. 
  Length, 
  one 
  inch 
  ; 
  height, 
  

   nine-tenths 
  of 
  an 
  inch. 
  

  

  Locality, 
  Williamsburg. 
  Miocene. 
  This 
  beautiful 
  shell 
  rarely 
  

   shows 
  the 
  concentric 
  ridges 
  perfect, 
  from 
  their 
  prominence 
  and 
  thin- 
  

   ness. 
  

  

  vol. 
  v. 
  — 
  4 
  I 
  

  

  