﻿386 
  

  

  E. 
  L. 
  Troxell 
  — 
  An 
  Oligocene 
  Camel. 
  

  

  Thus 
  the 
  third 
  premolars 
  both 
  above 
  and 
  below 
  are 
  of 
  

   exceptional 
  interest 
  in 
  the 
  formation 
  of 
  cusps 
  and 
  grooves. 
  It 
  

   has 
  been 
  pointed 
  out 
  (Scott) 
  that 
  in 
  many 
  animals 
  the 
  premolars 
  

   may 
  be 
  even 
  more 
  complicated 
  than 
  the 
  molars. 
  

  

  P 
  4 
  is 
  in 
  almost 
  every 
  detail 
  like 
  P 
  3 
  except 
  that 
  it 
  is 
  broader, 
  

   especially 
  posteriorly 
  where 
  it 
  meets 
  the 
  first 
  true 
  molar, 
  and 
  is 
  

  

  Fig. 
  3. 
  

  

  Fig. 
  4. 
  

  

  I^P 
  Pr 
  

   Cini 
  h^X 
  ,' 
  

  

  De 
  f 
  If 
  Deut 
  

  

  H 
  t 
  s 
  ' 
  " 
  7^1x5^^ 
  " 
  " 
  p 
  as 
  

  

  Trit 
  i 
  Trit 
  

   Pr 
  

  

  Met 
  

  

  Fig. 
  3. 
  Left, 
  upper, 
  third 
  niolar 
  of 
  Poebrotherium 
  andersoni 
  n. 
  sp., 
  

   natural 
  size. 
  (Cusp 
  nomenclature 
  according 
  to 
  Osborn's 
  Evolution 
  of 
  Mam- 
  

   malian 
  Molar 
  Teeth, 
  1907.) 
  Pr, 
  protocone 
  ; 
  Hy, 
  hypocone 
  or 
  enlarged 
  

   metaconule; 
  Met, 
  metacone; 
  Pa, 
  paracone; 
  Pas, 
  parastyle; 
  Ms, 
  mesostyle; 
  

   Mts, 
  rnetast3 
  T 
  le; 
  Pop, 
  internal, 
  basal 
  pillar: 
  Cing, 
  cingulum; 
  L, 
  lakes. 
  

  

  Fig. 
  4. 
  Left, 
  upper, 
  third 
  and 
  fourth 
  premolars, 
  natural 
  size. 
  Pr, 
  proto- 
  

   cone; 
  Pa, 
  paracone; 
  Deut, 
  deuterocone; 
  Trit, 
  tritocone; 
  Tet, 
  tetartocone. 
  

  

  Fig. 
  5. 
  

  

  Fig. 
  6. 
  

  

  Tal 
  

  

  Tet 
  

  

  '"Deut 
  

  

  Fig. 
  5. 
  Left, 
  lower, 
  third 
  molar, 
  natural 
  size. 
  Pr, 
  protoconid; 
  Met, 
  

   metaconid; 
  Pnt, 
  entoconid 
  ; 
  Hy, 
  hvpoconid; 
  Tal, 
  talonid 
  or 
  hypoconulid. 
  

  

  Fig. 
  6. 
  Left, 
  lower, 
  third 
  and 
  fourth 
  premolars, 
  natural 
  size. 
  Pr, 
  proto- 
  

   conid: 
  Pa, 
  paraconid; 
  Hy, 
  hypoconid 
  (metaconid 
  or 
  tritoconid 
  of 
  Scott); 
  

   Tet. 
  entoconid 
  (tetartoconid 
  of 
  Scott) 
  ; 
  Deut, 
  metaconid 
  (deuteroconid 
  of 
  

   Scott). 
  

  

  worn 
  down 
  to 
  a 
  greater 
  extent. 
  The 
  lake 
  in 
  the 
  hinder 
  portion 
  

   is 
  almost 
  obliterated, 
  but 
  still 
  retains 
  the 
  internal 
  outlet. 
  The 
  

   elements 
  of 
  the 
  wide 
  heel 
  may 
  be 
  identified 
  as 
  the 
  entoconid 
  

   and 
  the 
  hypoconid 
  of 
  Osborn 
  (tritoconid 
  and 
  tetartoconid 
  of 
  

   Scott). 
  

  

  Molars. 
  — 
  In 
  each 
  of 
  the 
  upper 
  molars 
  the 
  anterior 
  lobe 
  is 
  

   the 
  broader, 
  except 
  in 
  M 
  1 
  where 
  they 
  are 
  about 
  equal, 
  and 
  thus 
  

   each 
  tooth 
  over-reaches 
  in 
  lateral 
  extent 
  the 
  adjacent 
  surface 
  

   of 
  the 
  tooth 
  before 
  it. 
  M 
  1 
  is 
  less 
  in 
  longitudinal 
  diameter 
  

   than 
  M 
  2 
  and 
  because 
  of 
  its 
  greater 
  time 
  of 
  wear 
  has 
  its 
  lakes 
  

   obliterated. 
  

  

  M 
  3 
  has 
  fairly 
  prominent 
  ribs 
  on 
  each 
  lobe 
  and 
  an 
  anterior, 
  a 
  

   median 
  and 
  a 
  posterior 
  style 
  ; 
  the 
  mesostyle 
  is 
  especially 
  sharp. 
  

  

  