﻿174 
  Twenty-eighth 
  Eepokt 
  ok 
  the 
  State 
  Museum. 
  

  

  pit, 
  with 
  a 
  smaller 
  accessory 
  one. 
  This 
  is 
  a 
  feature 
  not 
  ob- 
  

   served 
  in 
  the 
  Waldron 
  specimens, 
  which 
  are 
  usually 
  found 
  as 
  

   the 
  exteriors 
  and 
  often 
  as 
  imperfect 
  interiors 
  of 
  the 
  valves 
  ; 
  

   the 
  few 
  casts 
  which 
  have 
  been 
  observed 
  from 
  this 
  locality, 
  

   do 
  not 
  show 
  -the 
  muscular 
  marking. 
  

  

  Surface 
  marked 
  by 
  strong 
  radiating 
  and 
  concentric 
  striae, 
  

   with 
  broad, 
  little 
  elevated, 
  radiating 
  ribs. 
  The 
  concentric 
  striae 
  

   of 
  growth 
  are 
  produced 
  into 
  prominent, 
  recurving, 
  fimbriated 
  

   laminae, 
  the 
  fimbriae 
  being 
  infolded 
  at 
  their 
  margins 
  and 
  bend- 
  

   ing 
  backward 
  in 
  the 
  form 
  of 
  long, 
  hollow, 
  semicylindrical 
  

   spines, 
  leading 
  a 
  broad 
  sinus 
  between, 
  in* 
  the 
  bottom 
  of 
  which 
  

   is 
  a 
  shorter 
  spine. 
  The 
  younger 
  specimens, 
  as 
  usually 
  pre- 
  

   served, 
  present 
  simple 
  fimbriated 
  lamellae. 
  

  

  MYTILARCA 
  Hall. 
  

   Mytilaeoa 
  siqilla 
  Hall. 
  

  

  Plate 
  27, 
  Fig/10. 
  

  

  Mytilarca 
  sigilJa. 
  Doc. 
  Edit. 
  28th 
  Rep. 
  St. 
  Mus. 
  Nat. 
  Hist. 
  Explanation 
  of 
  pi. 
  

   27, 
  fig. 
  10. 
  1876. 
  

  

  Body 
  of 
  the 
  shell 
  ovate-acute, 
  broadly 
  rounded 
  at 
  the 
  base 
  

   alate 
  posteriorly 
  ; 
  hinge-line 
  oblique. 
  Length 
  sixteen 
  milli- 
  

   metres. 
  

  

  The 
  specimen 
  is 
  a 
  cast 
  of 
  the 
  interior, 
  and 
  the 
  surface-mark- 
  

   ings 
  are 
  unknown. 
  

  

  CYPRICARDINIA 
  Hall. 
  

   Cypricardinia 
  arata. 
  

  

  Cypricardinia 
  arata 
  Hall,. 
  20th 
  Rep. 
  St. 
  Cab. 
  Nat. 
  Hist., 
  p. 
  337, 
  plate 
  14, 
  fig. 
  6. 
  

   1867. 
  Rev. 
  Edit., 
  p. 
  385. 
  1870. 
  

  

  Compare 
  Cypricardinia 
  subovata 
  Miller 
  and 
  Dyer. 
  ^Contributions 
  to 
  Palaeon- 
  

   tology, 
  No. 
  2. 
  1878. 
  

  

  Shell 
  subovate, 
  varying 
  from 
  moderately 
  to 
  extremely 
  gib- 
  

   bous, 
  slightly 
  alate 
  at 
  thepostero-cardinal 
  margin 
  ; 
  beaks 
  near 
  

   the 
  anterior 
  end, 
  which 
  is 
  short 
  and 
  rounded. 
  Surface 
  marked 
  

   by 
  strong 
  concentric 
  lamellose 
  ridges. 
  

  

  The 
  specimens 
  from 
  Waldron 
  present 
  no 
  marks 
  of 
  specific 
  

   distinction 
  from 
  those 
  of 
  the 
  Niagara 
  limestone 
  of 
  Wisconsin. 
  

  

  