﻿332 
  CONTRIBUTIONS 
  TO 
  THE 
  GEOLOGY 
  OP 
  

  

  Natica 
  perspectives 
  

  

  25. 
  Shell 
  subglobose, 
  smooth 
  ; 
  substance 
  of 
  the 
  shell 
  rather 
  thin 
  ; 
  

   umbilicus 
  open, 
  with 
  a 
  rather 
  prominent 
  revolving 
  rib, 
  considerably 
  

   above 
  the 
  middle 
  of 
  each 
  volution, 
  terminating 
  at 
  the 
  labrum 
  in 
  a 
  

   scarcely%listinct 
  callus 
  ; 
  spire 
  somewhat 
  elevated 
  and 
  acute 
  ; 
  aperture 
  

   semicircular, 
  five-eighths 
  the 
  length 
  of 
  the 
  shell. 
  Length, 
  eight-tenths 
  

   of 
  an 
  inch. 
  

  

  Locality, 
  Williamsburg. 
  Miocene. 
  This 
  shell 
  resembles 
  somewhat 
  

   the 
  N. 
  interna, 
  but 
  it 
  is 
  obviously 
  different 
  in 
  being 
  less 
  depressed, 
  and 
  

   in 
  the 
  form 
  and 
  proportions 
  of 
  the 
  aperture 
  ; 
  the 
  general 
  contour 
  of 
  the 
  

   shftll 
  is 
  also 
  different. 
  

  

  Fissurella 
  catilliformis. 
  

  

  26. 
  Shell 
  nearly 
  elliptical, 
  slightly 
  subovate, 
  depressed, 
  conic, 
  with 
  

   approximate 
  very 
  regular 
  longitudinal 
  costae, 
  alternated 
  with 
  inter- 
  

   vening 
  striae 
  often 
  very 
  minute, 
  the 
  transverse 
  concentric 
  striae 
  giv- 
  

   ing 
  a 
  very 
  uniform 
  granulation 
  to 
  the 
  costae; 
  foramen, 
  oval, 
  scarcely 
  

   inclined 
  ; 
  inner 
  margin 
  of 
  aperture 
  entire. 
  Length, 
  half 
  an 
  inch. 
  

  

  Locality, 
  Shell 
  banks, 
  Prince 
  George 
  county. 
  Miocene. 
  This 
  shell 
  

   has 
  some 
  resemblance 
  in 
  its 
  inner 
  surface 
  to 
  the 
  cavity 
  of 
  a 
  dish. 
  

  

  Area 
  protracta. 
  

  

  27. 
  Shell 
  rather 
  thick, 
  very 
  oblong 
  transversely 
  ; 
  ribs 
  about 
  forty, 
  

   not 
  very 
  prominent, 
  and 
  hardly 
  wider 
  than 
  the 
  intercostal 
  spaces, 
  and 
  

   longitudinally 
  furrowed 
  by 
  three 
  narrow 
  grooves, 
  the 
  central 
  one 
  much 
  

   the 
  widest; 
  a 
  very 
  indistinct 
  granulation 
  on 
  the 
  ribs, 
  arising 
  from 
  

   the 
  numerous 
  minute 
  transverse 
  lines 
  of 
  growth 
  crossing 
  the 
  longitu- 
  

   dinal 
  ridges 
  of 
  the 
  ribs; 
  beaks 
  prominent 
  and 
  distant, 
  opposite 
  a 
  point 
  

   less 
  than 
  one-third 
  the 
  length 
  of 
  the 
  hinge 
  margin 
  from 
  the 
  posterior 
  

   extremity; 
  area 
  wide, 
  with 
  numerous 
  distinct 
  undulated 
  grooves, 
  

   parallel 
  to 
  the 
  hinge 
  margin 
  ; 
  hinge 
  margin 
  rectilinear, 
  with 
  nume- 
  

   rous 
  minute 
  straight 
  teeth, 
  those 
  in 
  the 
  anterior 
  half 
  directed 
  a 
  little 
  

   obliquely 
  towards 
  the 
  anterior 
  margin; 
  posterior 
  margin 
  rounded 
  

   slightly 
  outwards, 
  extending 
  a 
  little 
  further 
  backward 
  than 
  the 
  angle 
  ; 
  

   anterior 
  margin 
  much 
  elongated, 
  extending 
  in 
  an 
  oval 
  curve 
  far 
  in 
  

  

  