﻿156 
  Twenty-eighth 
  Keport 
  on 
  the 
  State 
  Museum. 
  

  

  below. 
  Ventral 
  valve 
  regularly 
  convex, 
  the 
  greatest 
  convexity 
  

   about 
  the 
  middle 
  of 
  the 
  shell, 
  somewhat 
  abruptly 
  curving 
  to 
  

   the 
  anterior 
  margin, 
  cardinal 
  angles 
  very 
  slightly 
  flattened. 
  

   Dorsal 
  valve 
  concave, 
  ventral 
  area 
  linear, 
  extending 
  to 
  the 
  

   hinge 
  extremities 
  ; 
  foramen 
  equal 
  in 
  height 
  to 
  the 
  ventral 
  area 
  

   and 
  wider 
  than 
  high. 
  Dorsal 
  area 
  indicated 
  only 
  by 
  the 
  

   thickness 
  of 
  the 
  shell. 
  

  

  Surface 
  marked 
  by 
  obscure 
  radiating 
  plications 
  which 
  are 
  

   broad 
  and 
  rounded 
  below, 
  and 
  obsolescent 
  toward 
  the 
  beak 
  ; 
  

   cardinal 
  margin 
  of 
  the 
  ventral 
  valve 
  ornamented 
  by 
  two 
  

   diverging 
  spines 
  on 
  each 
  side 
  of 
  the 
  beak. 
  

  

  This 
  species 
  is 
  especially 
  characterized 
  by 
  the 
  rounded 
  pli- 
  

   cations, 
  which 
  are 
  frequently 
  obscure 
  and 
  often 
  obsolescent 
  on 
  

   the 
  center 
  of 
  the 
  valve, 
  where 
  they 
  appear 
  as 
  simple 
  undula- 
  

   tions 
  of 
  the 
  surface. 
  The 
  bases 
  of 
  two 
  spines 
  on 
  each 
  side 
  of 
  

   the 
  beak 
  are 
  usually 
  preserved, 
  and 
  no 
  specimen 
  examined 
  

   has 
  shown 
  more 
  than 
  that 
  number. 
  

  

  SPIR1FERA 
  Sowerby. 
  

   Spirifera 
  Eudora. 
  

  

  Plate 
  24, 
  Figs 
  13-18. 
  

  

  Spirifer 
  Eudora 
  Hall. 
  Ann. 
  Geolog. 
  Report 
  Wisconsin. 
  1861. 
  

  

  Spirifer 
  Eudora 
  Hall. 
  Trans. 
  Alb. 
  Inst., 
  vol. 
  iv, 
  p. 
  211. 
  Abstraot 
  p. 
  17: 
  May, 
  1863. 
  

  

  Spirif 
  era 
  Eudora 
  Hall. 
  20th 
  Rept. 
  State 
  Cab. 
  Nat. 
  Hist., 
  p. 
  370, 
  pi. 
  13, 
  figs. 
  5, 
  7. 
  

  

  1867. 
  Revised 
  Edit., 
  p. 
  377, 
  pi. 
  13, 
  figs. 
  5, 
  7. 
  [1870.] 
  

   Compare 
  S. 
  Niagarensis 
  var. 
  oligoptycha 
  F. 
  Roemer. 
  Sil. 
  Faun. 
  Westl. 
  Tenn., 
  p. 
  

  

  68, 
  pi. 
  5, 
  fig. 
  8. 
  

  

  This 
  species 
  was 
  originally 
  described 
  from 
  casts 
  from 
  the 
  

   limestone 
  of 
  Racine, 
  Wisconsin. 
  The 
  casts 
  show 
  a 
  higher 
  

   area 
  than 
  the 
  entire 
  specimens, 
  since 
  the 
  strongly 
  incurved 
  

   beak 
  of 
  the 
  ventral 
  valve 
  covers 
  much 
  of 
  the 
  area, 
  giving 
  a 
  

   less 
  distance 
  between 
  the 
  beaks 
  of 
  the 
  opposite 
  valves 
  than 
  

   is 
  shown 
  in 
  the 
  casts. 
  The 
  surface 
  is 
  marked 
  by 
  line 
  radi- 
  

   ating 
  striae, 
  which 
  are 
  precisely 
  of 
  the 
  character 
  of 
  those 
  of 
  

   S. 
  macropleura 
  of 
  the 
  lower 
  Helderberg 
  group. 
  

  

  The 
  species 
  given 
  by 
  Roemer 
  as 
  S. 
  Niagarensis 
  var. 
  oli- 
  

   goptycha 
  differs 
  from 
  this 
  species 
  in 
  the 
  proportionally 
  longer 
  

   hinge-line 
  ; 
  and 
  when 
  compared 
  with 
  specimens 
  of 
  8. 
  macro- 
  

   pleura 
  from 
  Tennessee, 
  presents 
  no 
  essential 
  differences 
  of 
  

   character. 
  

  

  