﻿NO. 
  1969. 
  FOUR 
  NEW 
  SPECIES 
  OF 
  FOSSIL 
  HORSES— 
  HAY. 
  591 
  

  

  A 
  study 
  of 
  the 
  arrangement 
  of 
  the 
  enamel 
  of 
  E. 
  laurentius 
  shows 
  

   that 
  it 
  is 
  much 
  like 
  that 
  of 
  E. 
  niobrarensis; 
  and 
  far 
  more 
  simple 
  

   than 
  in 
  E. 
  complicatus. 
  The 
  contiguous 
  ends 
  of 
  the 
  two 
  lakes 
  are 
  

   about 
  as 
  much 
  folded 
  as 
  in 
  E. 
  niobrarensis, 
  probably 
  more 
  so. 
  The 
  

   post-protoconal 
  valley 
  differs 
  from 
  that 
  of 
  the 
  latter 
  species, 
  being 
  

   narrower 
  and 
  almost 
  without 
  a 
  reentering 
  loop 
  at 
  its 
  irmer 
  end. 
  

   Moreover, 
  it 
  is 
  directed 
  more 
  nearly 
  forward, 
  and 
  its 
  extremity 
  does 
  

   not 
  reach 
  the 
  center 
  of 
  the 
  tooth. 
  

  

  In 
  the 
  lower 
  jaw 
  the 
  cheek 
  teeth 
  have 
  the 
  enamel 
  bands 
  less 
  

   crinkled 
  than 
  in 
  E. 
  niobrarensis. 
  They 
  differ 
  from 
  the 
  latter 
  in 
  

   another 
  respect. 
  At 
  the 
  middle 
  of 
  the 
  length 
  of 
  the 
  outer, 
  or 
  buccal 
  

   face 
  of 
  the 
  tooth, 
  there 
  is 
  a 
  reentering 
  loop, 
  or 
  valley, 
  of 
  enamel. 
  In 
  

   the 
  species 
  here 
  described 
  it 
  will 
  be 
  seen 
  that 
  this 
  valley 
  pushes 
  itself 
  

   in 
  between 
  the 
  adjacent 
  ends 
  of 
  the 
  two 
  loops 
  of 
  enamel 
  that 
  run 
  

   longitudinally 
  near 
  the 
  middle 
  of 
  the 
  tooth. 
  Only 
  in 
  the 
  two 
  anterior 
  

   premolars 
  does 
  this 
  relation 
  of 
  the 
  loops 
  fail 
  to 
  develop. 
  In 
  the 
  type 
  

   of 
  E. 
  niobrarensis 
  the 
  longitudinal 
  loops 
  wholly 
  exclude 
  the 
  outer 
  

   loop. 
  It 
  will 
  be 
  noted 
  further 
  that 
  the 
  outer 
  loop 
  in 
  E. 
  niobrarensis 
  

   is 
  pretty 
  deeply 
  notched 
  in 
  its 
  hinder 
  side. 
  The 
  lower 
  teeth 
  of 
  E. 
  

   laurentius 
  resemble, 
  with 
  respect 
  to 
  the 
  loops, 
  those 
  of 
  E. 
  caballus; 
  

   but 
  those 
  of 
  the 
  latter 
  have 
  a 
  notch 
  in 
  the 
  hinder 
  border 
  of 
  the 
  outer 
  

   loop. 
  It 
  -svill 
  be 
  observed 
  that 
  the 
  teeth 
  of 
  E. 
  laurentius 
  are 
  smaller 
  

   than 
  those 
  of 
  E. 
  niobrarensis. 
  

  

  In 
  differentiating 
  the 
  present 
  species 
  from 
  E. 
  excelsus 
  Leidy 
  we 
  

   are, 
  at 
  present, 
  limited 
  to 
  comparison 
  with 
  the 
  type 
  specimen 
  of 
  the 
  

   latter. 
  This 
  is 
  in 
  the 
  United 
  States 
  National 
  Museum. 
  It 
  was 
  

   figured 
  by 
  Leidy 
  ^ 
  and 
  again 
  by 
  Gidley.' 
  It 
  consists 
  of 
  a 
  fragment 
  of 
  

   the 
  right 
  maxilla 
  and 
  the 
  last 
  upper 
  premolar 
  and 
  the 
  three 
  molars. 
  

   These 
  four 
  teeth 
  measure 
  in 
  length 
  but 
  a 
  little 
  more 
  than 
  the 
  corre- 
  

   sponding 
  teeth 
  of 
  E. 
  laurentius. 
  Three 
  differences 
  in 
  the 
  arrangement 
  

   of 
  the 
  enamel 
  are 
  noted 
  between 
  the 
  two 
  species. 
  (1) 
  In 
  E. 
  laurentius 
  

   the 
  post-protoconal 
  valley 
  keeps 
  closer 
  to 
  the 
  lingual 
  side 
  of 
  the 
  tooth 
  

   than 
  in 
  E. 
  excelsus. 
  (2) 
  In 
  the 
  latter 
  species 
  the 
  front 
  border 
  of 
  the 
  

   anterior 
  lake 
  is 
  without 
  notch 
  and 
  it 
  swings 
  backward 
  in 
  a 
  curve 
  to 
  

   near 
  the 
  head 
  of 
  the 
  post-protoconal 
  valley 
  and 
  then 
  turns 
  abruptly 
  

   outward 
  to 
  form 
  a 
  notch. 
  In 
  E. 
  laurentius 
  tliis 
  front 
  border 
  is 
  con- 
  

   spicuously 
  notched; 
  while, 
  facing 
  the 
  head 
  of 
  the 
  post-protoconal 
  

   valley, 
  the 
  border 
  rounds 
  backward 
  and 
  outward 
  to 
  form 
  a 
  notch 
  

   that 
  is 
  often 
  M 
  -shaped. 
  (3) 
  Both 
  the 
  front 
  and 
  the 
  hinder 
  borders 
  of 
  

   the 
  posterior 
  lake 
  are 
  more 
  deeply 
  notched 
  than 
  in 
  E. 
  excelsus. 
  In 
  

   general, 
  there 
  is 
  in 
  E. 
  laurentius 
  a 
  higher 
  degree 
  of 
  complication 
  of 
  

   the 
  enamel 
  than 
  in 
  E. 
  excelsus. 
  

  

  • 
  Ext. 
  Mamm. 
  Fauna 
  Dak. 
  and 
  Nebr., 
  pi. 
  21, 
  fig. 
  31 
  . 
  

   ' 
  Bull. 
  Amer. 
  Mus. 
  Nat. 
  Hist., 
  vol. 
  14, 
  p. 
  114, 
  fig. 
  9. 
  

  

  