﻿396 
  E. 
  L. 
  Troxell 
  — 
  A 
  Tiny 
  Oligocene 
  Artiodactyl. 
  

  

  information 
  would 
  be 
  of 
  especial 
  benefit 
  in 
  distinguish- 
  

   ing 
  the 
  species. 
  5 
  

  

  The 
  lower 
  jaw 
  is 
  slender, 
  and, 
  judged 
  from 
  the 
  imprint 
  

   in 
  the 
  matrix, 
  it 
  has 
  a 
  long 
  ascending 
  ramus 
  which 
  slopes 
  

   backward 
  considerably 
  as 
  in 
  the 
  Camelidse. 
  

  

  Hypisodus 
  minimus 
  Cope. 
  

   (Fig. 
  4.) 
  

  

  In 
  this 
  specimen, 
  Cat. 
  No. 
  10034, 
  Yale 
  Collection, 
  a 
  

   portion 
  of 
  the 
  maxillary 
  with 
  the 
  tooth 
  series 
  P 
  3 
  - 
  4 
  , 
  M 
  1 
  - 
  2 
  - 
  3 
  , 
  

   shows 
  some 
  very 
  marked 
  differences 
  from 
  that 
  of 
  the 
  

   skull 
  just 
  described. 
  In 
  size 
  it 
  compares 
  well 
  with 
  the 
  

   type 
  of 
  H. 
  minimus. 
  The 
  molars 
  exhibit 
  no 
  basal 
  

   shoulder 
  but 
  have 
  distinct 
  roots. 
  They 
  are 
  hypsodont, 
  

   except 
  perhaps 
  M 
  1 
  , 
  which 
  is 
  slightly 
  more 
  worn 
  and 
  

  

  Fig. 
  4. 
  

  

  Fig. 
  4. 
  — 
  Crown 
  view 
  of 
  upper 
  molars 
  and 
  premolars 
  of 
  Hypisodus 
  minimus 
  

   Cope. 
  Cat. 
  No. 
  10034, 
  Yale 
  Fossil 
  Vertebrate 
  Collection. 
  Twice 
  natural 
  

   size. 
  

  

  may 
  be 
  said 
  to 
  be 
  subhypsodont; 
  this 
  tooth 
  is 
  smaller 
  

   than 
  M 
  3 
  . 
  

  

  A 
  minute 
  sharp 
  internal 
  folding 
  from 
  the 
  posterior 
  

   corner 
  of 
  the 
  protocone 
  may 
  be 
  seen 
  on 
  M 
  1 
  - 
  2 
  , 
  but 
  none 
  

   appears 
  on 
  M 
  3 
  . 
  This 
  is 
  similar 
  to 
  an 
  internal 
  basal 
  

   pillar, 
  but 
  is 
  not 
  basal 
  in 
  position. 
  The 
  valley 
  between 
  

   the 
  internal 
  lobes 
  in 
  M 
  3 
  is 
  wide 
  and 
  open. 
  

  

  The 
  fourth 
  premolar 
  resembles 
  that 
  of 
  Leptomeryx 
  

   rather 
  than 
  that 
  of 
  Poebrotherium, 
  the 
  deuterocone 
  being 
  

   compressed 
  longitudinally 
  so 
  as 
  to 
  give 
  the 
  tooth 
  the 
  

   form 
  of 
  a 
  triangle. 
  This 
  cone 
  is 
  not 
  high 
  but 
  is 
  situated 
  

  

  5 
  In 
  all 
  other 
  specimens 
  at 
  hand, 
  the 
  more 
  typical 
  premolar 
  has 
  three 
  

   cusps, 
  the 
  paraeonid, 
  protoeonid 
  and 
  hypoconid 
  appearing 
  distinct 
  on 
  the 
  

   outer 
  side. 
  These 
  premolars 
  have 
  the 
  appearance 
  of 
  milk 
  teeth 
  in 
  the 
  later 
  

   forms, 
  but 
  we 
  would 
  not 
  expect 
  to 
  find 
  unworn 
  milk 
  teeth 
  in 
  a 
  ramus 
  along 
  

   with 
  well 
  worn 
  molars 
  ; 
  furthermore, 
  they 
  are 
  not 
  three-' 
  ' 
  lobed 
  ' 
  ' 
  but 
  simply 
  

   have 
  the 
  three 
  cusps 
  — 
  para-, 
  proto-, 
  and 
  hypoconid 
  — 
  accentuated, 
  a 
  condi- 
  

   tion 
  which 
  we 
  find 
  in 
  Poebrotherium 
  and 
  other 
  forms. 
  Along 
  with 
  this 
  type 
  

   of 
  fourth 
  premolar, 
  in 
  the 
  other 
  specimens, 
  we 
  find 
  P 
  3 
  with 
  the 
  same 
  general 
  

   composition 
  of 
  cusps, 
  but 
  of 
  reduced 
  size. 
  

  

  