﻿E. 
  L. 
  Troxell 
  — 
  An 
  Oligocene 
  Camel. 
  381 
  

  

  Art. 
  XXXIV. 
  — 
  An 
  Oligocene 
  Camel, 
  Poebrotherium 
  ander- 
  

   soni 
  n. 
  sp. 
  ; 
  by 
  Edward 
  L. 
  Troxell. 
  

  

  Contents. 
  

  

  Introduction 
  ; 
  Summary 
  and 
  conclusions 
  ; 
  Observations 
  on 
  the 
  skull, 
  

   teeth 
  and 
  atlas 
  ; 
  Related 
  forms 
  ; 
  Similarities 
  and 
  distinctions 
  ; 
  

   Measurements 
  and 
  Bibliography. 
  

  

  Introduction. 
  — 
  The 
  osteology 
  of 
  the 
  skull 
  of 
  Po'ebrotherium 
  

   has 
  been 
  given, 
  especially 
  by 
  Scott, 
  1891, 
  and 
  Wortman, 
  1898 
  ; 
  

   therefore 
  only 
  the 
  features 
  of 
  interest 
  which 
  are 
  seen 
  in 
  the 
  

   new 
  specimen 
  and 
  the 
  differences 
  between 
  it 
  and 
  the 
  known 
  

   species 
  will 
  be 
  discussed 
  in 
  the 
  following 
  pages. 
  

  

  The 
  specimen, 
  a 
  nearly 
  complete 
  skull, 
  jaws 
  and 
  atlas, 
  found 
  

   near 
  Harrison, 
  Nebraska, 
  comes 
  from 
  the 
  Oligocene, 
  Oreodon 
  

   Zone 
  and 
  was 
  contemporaneous 
  with, 
  and 
  about 
  the 
  size 
  of 
  

   Mesohippus, 
  the 
  early 
  three-toed 
  horse. 
  

  

  Summary 
  and 
  conclusions. 
  — 
  As 
  a 
  result 
  of 
  the 
  study 
  of 
  the 
  

   specimen, 
  the 
  following 
  points 
  present 
  themselves: 
  

  

  The 
  upper 
  canine 
  is 
  very 
  small, 
  but 
  the 
  third 
  incisor, 
  greatly 
  

   enlarged, 
  performs 
  the 
  function 
  of 
  a 
  canine. 
  Especially 
  long 
  

   diastemas 
  bound 
  the 
  first 
  premolars, 
  both 
  in 
  the 
  upper 
  and 
  

   lower 
  jaws, 
  thus 
  sharply 
  distinguishing 
  the 
  species 
  from 
  

   Po'ebrotherium 
  eximium. 
  A 
  cingular 
  ridge 
  and 
  an 
  internal 
  

   basal 
  pillar 
  on 
  M 
  3 
  , 
  as 
  well 
  as 
  the 
  cusps 
  and 
  grooves 
  in 
  the 
  third 
  

   premolars, 
  above 
  and 
  below, 
  are 
  characters 
  not 
  usually 
  found 
  

   in 
  Poebrotherium. 
  

  

  The 
  cement 
  coating 
  on 
  the 
  lower 
  molars, 
  and 
  also 
  their 
  

   straight, 
  perpendicular 
  sides 
  and 
  long 
  enamel 
  covering 
  — 
  a 
  first 
  

   step 
  toward 
  hypsodonty 
  — 
  indicates 
  an 
  animal 
  of 
  considerable 
  

   advancement. 
  Posteriorly 
  the 
  orbit 
  is 
  not 
  inclosed 
  with 
  a 
  bony 
  

   ring 
  as 
  in 
  Gomphotherium 
  and 
  the 
  later 
  camels 
  ; 
  this 
  is 
  a 
  

   primitive 
  character. 
  

  

  The 
  present 
  specimen 
  shows 
  so 
  many 
  features 
  not 
  found 
  in 
  

   the 
  other 
  related 
  forms, 
  that 
  it 
  is 
  here 
  made 
  the 
  type 
  of 
  a 
  new 
  

   species 
  : 
  Poebrotherium 
  andersoni* 
  

  

  Morphology. 
  — 
  The 
  wdiole 
  skull 
  and 
  jaws 
  are 
  long 
  and 
  

   slender, 
  a 
  form 
  made 
  possible, 
  partly 
  by 
  the 
  short 
  crowned 
  

   teeth 
  and 
  partly 
  by 
  the 
  diastemata 
  before 
  and 
  behind 
  the 
  first 
  

   premolars. 
  

  

  A 
  conspicuous 
  feature 
  in 
  these 
  early 
  camels 
  is 
  the 
  large 
  otic 
  

   bulla. 
  In 
  the 
  genus 
  generally 
  it 
  is 
  large 
  and 
  round, 
  but 
  in 
  

   the 
  present 
  specimen, 
  which 
  in 
  this 
  respect 
  resembles 
  the 
  later 
  

   camels, 
  the 
  form 
  is 
  roughly 
  triangular 
  and 
  consists 
  of 
  two 
  por- 
  

  

  *Note 
  : 
  The 
  species 
  is 
  named 
  in 
  honor 
  of 
  Mr. 
  John 
  Anderson 
  of 
  Harrison, 
  

   Nebraska, 
  who, 
  because 
  of 
  his 
  keen 
  interest 
  in 
  natural 
  science 
  and 
  his 
  exceed- 
  

   ing 
  generosity, 
  has 
  been 
  of 
  such 
  great 
  assistance 
  to 
  western 
  explorers. 
  

  

  