﻿NO. 
  1969. 
  FOUR 
  NEW 
  SPECIES 
  OF 
  FOSSIL 
  HORSES— 
  HAY. 
  593 
  

  

  It 
  must 
  be 
  observed 
  that 
  these 
  teeth, 
  as 
  shown 
  by 
  the 
  reduced 
  height, 
  

   are 
  more 
  worn 
  than 
  those 
  of 
  the 
  type. 
  Hence, 
  each 
  one 
  originaUy 
  

   had 
  the 
  grindmg 
  surface 
  possibly 
  shghtly 
  longer 
  than 
  it 
  now 
  is. 
  It 
  

   will 
  be 
  seen 
  that 
  the 
  front 
  border 
  of 
  most 
  of 
  the 
  anterior 
  lakes 
  is 
  

   slightly 
  notched 
  and 
  likewise 
  the 
  hinder 
  border 
  of 
  some 
  of 
  the 
  posterior 
  

   lakes. 
  The 
  post-pro 
  toconal 
  valleys 
  resemble 
  those 
  of 
  the 
  type 
  of 
  

   E. 
  excelsus. 
  

  

  Figure 
  24 
  presents 
  a 
  view 
  of 
  the 
  left 
  lower 
  milk 
  molars 
  of 
  a 
  jaw, 
  

   No. 
  2758, 
  from 
  Hay 
  Springs, 
  now 
  in 
  the 
  American 
  Museum 
  of 
  Natural 
  

   History. 
  This 
  jaw 
  belonged 
  to 
  a 
  colt 
  of 
  practically 
  

   the 
  same 
  age 
  as 
  the 
  jaw. 
  No. 
  2757, 
  described 
  under 
  \*^Vi^^V\ 
  

   E. 
  niohrarensis, 
  but 
  slightly 
  younger, 
  il/.i 
  is 
  in 
  j 
  / 
  J 
  A 
  

   use; 
  m.2 
  is 
  not 
  quite 
  through 
  the 
  bone; 
  the 
  perma- 
  /v-^""^ 
  -^ 
  

   nent 
  incisors 
  had 
  not 
  begun 
  to 
  wear. 
  The 
  jaw 
  is 
  \Vi\ 
  VX' 
  

   100 
  mm. 
  shorter 
  than 
  that 
  numbered 
  2757. 
  JdJ^ 
  ' 
  

  

  Measurements 
  of 
  lower 
  jaws. 
  . 
  , 
  

  

  mm. 
  ) 
  

  

  Front 
  of 
  jaw 
  to 
  rear 
  of 
  ascending 
  ramus 
  360 
  ^^^^^ 
  ^^ 
  I' 
  

  

  Length 
  of 
  symphysis 
  63 
  v 
  

  

  Height 
  of 
  jaw 
  at 
  front 
  of 
  dm.^ 
  60 
  \)^/^ 
  I 
  ( 
  

  

  Height 
  of 
  jaw 
  at 
  rear 
  of 
  rfm.4 
  76 
  — 
  -^—/Sl,-'' 
  28 
  

  

  Height 
  of 
  condyle 
  above 
  lower 
  border 
  of 
  jaw 
  220 
  

  

  Dm.r,, 
  length 
  32 
  

  

  width 
  12 
  

  

  Dm. 
  3, 
  length 
  30 
  

  

  width 
  13 
  \ 
  Y 
  M^ 
  I 
  « 
  

  

  Z)to.4, 
  length 
  32 
  ^j.< 
  y^ 
  .C 
  H/ 
  

  

  width 
  12 
  CC^' 
  

  

  if.„length 
  32 
  Jjji 
  

  

  width 
  11 
  rQ^ 
  ' 
  

  

  It 
  is 
  probable 
  that 
  most 
  of 
  these 
  teeth, 
  espe- 
  

   cially 
  the 
  last 
  milk 
  molar 
  and 
  the 
  first 
  true 
  molar, 
  

  

  have 
  the 
  grinding 
  surface 
  longer 
  than 
  it 
  would 
  have 
  

  

  ° 
  ,. 
  , 
  Y 
  p 
  Fig. 
  28.— 
  EQm:s 
  excel- 
  

  

  been 
  at 
  a 
  nttle 
  later 
  stage 
  01 
  wear; 
  and 
  the 
  true 
  sus. 
  last 
  premolar 
  

   molar 
  is 
  narrower 
  than 
  it 
  would 
  have 
  been 
  later. 
  ^'^ 
  ™^^^ 
  molars 
  of 
  

  

  . 
  J, 
  , 
  ■^^ 
  1 
  '11 
  RIGHT 
  SIDE 
  OF 
  TTPPER 
  

  

  On 
  companson 
  of 
  these 
  milk 
  molars 
  with 
  those 
  jaw. 
  x 
  |. 
  "112," 
  

   supposed 
  to 
  belong 
  to 
  E. 
  niohrarensis, 
  it 
  will 
  be 
  ^^^^- 
  ^"^- 
  ^'*-^- 
  

   seen 
  that 
  the 
  latter 
  are 
  both 
  longer 
  and 
  consider- 
  

   ably 
  broader. 
  Also 
  the 
  median 
  outer 
  vaUey 
  pushes 
  in 
  between 
  the 
  

   longitudinal 
  valleys, 
  whereas 
  they 
  fail 
  to 
  do 
  so 
  in 
  No. 
  2758. 
  

  

  It 
  is 
  impossible 
  to 
  refer 
  this 
  jaw 
  with 
  certainty 
  to 
  any 
  described 
  

   species, 
  but 
  it 
  seems 
  more 
  probable 
  that 
  it 
  belongs 
  to 
  E. 
  excelsus 
  

   than 
  to 
  any 
  other 
  known 
  species. 
  It 
  may 
  be 
  stated 
  that 
  among 
  the 
  

   Hay 
  Springs 
  horses 
  was 
  one 
  whose 
  lower 
  premolars 
  and 
  molars 
  formed 
  

   a 
  row 
  even 
  longer 
  than 
  that 
  of 
  E. 
  niohrarensis; 
  but 
  these 
  teeth 
  were 
  

   much 
  narrower. 
  

  

  69077°^Proc.N.M.vol.44— 
  13 
  38 
  

  

  