﻿E. 
  L. 
  Troxell 
  — 
  A 
  Tiny 
  Oligocene 
  Artiodactyl. 
  397 
  

  

  so 
  low 
  on 
  the 
  inner 
  side 
  of 
  the 
  tooth 
  that 
  in 
  a 
  well-worn 
  

   specimen 
  it 
  is 
  still 
  distinct 
  enough 
  to 
  remain 
  separated 
  

   and 
  posterior. 
  P 
  3 
  , 
  almost 
  brachyodont, 
  is 
  compressed 
  

   and 
  trenchant, 
  but 
  yet 
  has 
  a 
  lake 
  entering 
  between 
  the 
  

   deuterocone 
  and 
  tetartocone 
  and 
  running 
  anteriorly 
  to 
  

   the 
  paracone 
  ; 
  in 
  this 
  it 
  resembles 
  P 
  4 
  . 
  On 
  the 
  molars 
  and 
  

   premolars 
  of 
  this 
  specimen 
  the 
  lakes 
  and 
  crevices 
  are 
  

   filled 
  with 
  cement. 
  

  

  Summary. 
  

  

  Because 
  of 
  the 
  difficulty 
  of 
  finding 
  and 
  collecting 
  the 
  

   parts 
  of 
  this 
  tiny 
  animal, 
  its 
  skeleton 
  is 
  not 
  very 
  well 
  

   known. 
  It 
  is 
  the 
  earliest 
  hypsodont 
  artiodactyl 
  yet 
  

   found. 
  

  

  In 
  attempts 
  at 
  classification, 
  it 
  has 
  been 
  placed 
  with 
  

   the 
  camels, 
  with 
  the 
  tragulids, 
  and 
  yet 
  again 
  separated 
  

   out 
  with 
  Stenomylus 
  to 
  form 
  an 
  aberrant 
  branch. 
  The 
  

   type 
  is 
  more 
  advanced 
  than 
  the 
  camels 
  of 
  the 
  same 
  

   period, 
  but 
  seems 
  to 
  fit 
  in 
  somewhere 
  near 
  Leptomeryx 
  

   or 
  Hypertragulus, 
  and 
  has 
  also 
  a 
  slight 
  resemblance 
  to 
  

   Heteromeryx. 
  

  

  Though 
  the 
  front 
  limb 
  is 
  not 
  known, 
  the 
  hind 
  foot, 
  

   generally 
  the 
  more 
  advanced 
  in 
  evolution, 
  still 
  retains 
  

   slender 
  metatarsals 
  II 
  and 
  V. 
  

  

  The 
  specimen 
  of 
  Hypisodus 
  minimus 
  Cope 
  in 
  the 
  

   Marsh 
  Collection 
  is 
  a 
  maxillary 
  with 
  five 
  teeth 
  (fig. 
  4) 
  ; 
  

   its 
  size 
  is 
  close 
  to 
  that 
  of 
  Cope's 
  type, 
  and 
  on 
  that 
  basis 
  

   it 
  will 
  be 
  classed 
  with 
  the 
  latter. 
  Several 
  distinguishing 
  

   features 
  of 
  the 
  teeth 
  may 
  be 
  enumerated 
  : 
  there 
  is 
  a 
  fold 
  

   on 
  the 
  posterior 
  side 
  of 
  the 
  protocone 
  of 
  both 
  M 
  1 
  and 
  M 
  2 
  ; 
  

   M 
  3 
  is 
  much 
  larger 
  than 
  M 
  1 
  or 
  M 
  2 
  ; 
  the 
  fourth 
  premolar 
  

   is 
  triangular; 
  P 
  3 
  is 
  short-crowned 
  and 
  trenchant; 
  and 
  

   there 
  is 
  a 
  coating 
  of 
  cement 
  on 
  many 
  parts. 
  

  

  Hypisodus 
  alacer, 
  sp. 
  nov., 
  figs. 
  1-3, 
  is 
  about 
  one- 
  

   seventh 
  smaller 
  than 
  the 
  type 
  of 
  TI. 
  minimus 
  Cope, 
  as 
  

   shown 
  by 
  applying 
  the 
  system 
  of 
  " 
  ratios.' 
  ' 
  The 
  teeth 
  

   are 
  simpler 
  than 
  those 
  of 
  the 
  other 
  species, 
  and 
  the 
  upper 
  

   molars 
  are 
  of 
  uniform 
  size, 
  M 
  3 
  being 
  one-fifth 
  smaller 
  

   than 
  Cope's 
  type. 
  Both 
  P 
  3 
  and 
  P 
  4 
  simulate 
  the 
  true 
  

   molars 
  in 
  having 
  two 
  lobes 
  each. 
  The 
  metastylid 
  is 
  

   well 
  shown, 
  and 
  the 
  posterior 
  lobe 
  of 
  P 
  4 
  is 
  molariform. 
  

  

  