﻿III] 
  Special 
  Report 
  No. 
  6 
  : 
  Midway 
  Eocene 
  Fauna 
  297 
  

  

  CEPHALOPODA 
  

  

  Ptychoceras, 
  near 
  crassum, 
  Plate 
  51, 
  fig. 
  5. 
  

  

  See 
  Rept. 
  Geol. 
  Black 
  Hills 
  of 
  Dakota, 
  by 
  Whitfield, 
  p. 
  459, 
  

   plate 
  16, 
  figs. 
  3-5, 
  1880. 
  See 
  also 
  Meek's 
  report 
  U. 
  S. 
  Geol. 
  

   Surv. 
  Terr., 
  vol. 
  9, 
  p. 
  412, 
  plate 
  20, 
  figs. 
  4a-d, 
  -P. 
  mortoni. 
  

   Locality- 
  R.ayburn's 
  salt 
  works. 
  

  

  Heteroceras 
  sp., 
  Plate 
  51, 
  fig. 
  4. 
  

  

  See 
  Turrilites 
  pauper 
  Witf., 
  U. 
  S. 
  Geol. 
  Surv., 
  Mon. 
  18, 
  p. 
  268, 
  

   plate 
  45, 
  figs 
  1-4. 
  

  

  We 
  do 
  not 
  feel 
  quite 
  satisfied 
  that 
  Heteroceras 
  is 
  the 
  name 
  that 
  

   will 
  finally 
  be 
  applied 
  to 
  sinistral 
  cephalopoda 
  of 
  this 
  type. 
  

   However, 
  this 
  is 
  a 
  very 
  interesting 
  specimen 
  and 
  deserves 
  to 
  be 
  

   figured 
  in 
  this 
  place. 
  

  

  /.^m///i'.-Rayburn's 
  salt 
  works. 
  

  

  Baculites 
  anceps, 
  Plate 
  51, 
  fig. 
  6. 
  

  

  Syn. 
  — 
  This 
  species 
  Stanton 
  has 
  regarded 
  as 
  anceps 
  of 
  I^amarck, 
  

   and 
  probably 
  regarded 
  it 
  as 
  synonymous 
  with 
  B. 
  asper 
  Morton. 
  

  

  Only 
  small 
  fragments 
  have 
  been 
  so 
  far 
  found. 
  They 
  show 
  

   the 
  low 
  undulations 
  of 
  asper 
  z.s 
  figured 
  by 
  Morton, 
  though 
  the 
  

   suture 
  line 
  is 
  not 
  determinable. 
  

  

  Z,^ra/zV}'. 
  -Ray 
  burn's 
  salt 
  works. 
  

  

  BRACHLOPODA 
  

  

  Terebratulina 
  sp., 
  Plate 
  51, 
  fig. 
  7. 
  

  

  We 
  have 
  not 
  seen 
  any 
  species 
  figured 
  that 
  looks 
  just 
  like 
  this. 
  

  

  Whitfield's 
  figures 
  of 
  Terebratella 
  vanuxemi 
  and 
  T. 
  plicata 
  from 
  

  

  N. 
  J. 
  have 
  much 
  coarser 
  costse. 
  The 
  same 
  is 
  true 
  of 
  T-sayi 
  

  

  Morton. 
  

  

  Z.^<:a/z'/>.-Rayburn's 
  salt 
  works. 
  

  

  Eocene 
  

  

  Midway 
  Stage 
  

  

  PELECYPODA 
  

  

  Ostrea 
  crenulimarginata, 
  Plate 
  52, 
  figs. 
  i. 
  a. 
  

  

  Syn. 
  O. 
  crenulimarginata 
  Gabb, 
  Jr. 
  Acad. 
  Nat. 
  Sci., 
  Phila., 
  

   2dser., 
  vol. 
  4, 
  p. 
  398, 
  plate 
  68, 
  figs. 
  40, 
  41, 
  i860. 
  

  

  