﻿340 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  VOL. 
  % 
  

  

  petrosal. 
  In 
  Limnocyon 
  and 
  Thinocyon 
  the 
  trough 
  is 
  more 
  widely 
  

   open 
  and 
  relatively 
  shorter. 
  The 
  petrosal 
  is 
  partially 
  exposed 
  

   on 
  both 
  sides 
  of 
  the 
  skull 
  of 
  M. 
  eothen. 
  It 
  exhibits 
  an 
  acutely 
  

   projecting 
  promontorium 
  located 
  immediately 
  inward 
  from 
  the 
  

   medial 
  margin 
  of 
  the 
  mastoid 
  process. 
  The 
  petrosal 
  is 
  more 
  

   broadly 
  rounded 
  ventrally 
  in 
  Thinocyon. 
  The 
  fenestra 
  rotunda 
  

   in 
  M. 
  eothen 
  is 
  large 
  and 
  faces 
  posteriorly 
  and 
  slightly 
  outward 
  

   and 
  downward 
  below 
  the 
  flattened 
  ventral 
  surface 
  of 
  the 
  pos- 
  

   terior 
  portion 
  of 
  the 
  petrosal. 
  The 
  anterior 
  surface 
  of 
  the 
  

   petrosal 
  is 
  broad 
  and 
  flattened, 
  facing 
  anterolaterally 
  and 
  ven- 
  

   trally 
  and 
  joining 
  the 
  medial 
  surface 
  in 
  a 
  bluntly 
  rounded 
  angle 
  

   that 
  extends 
  anteromedially 
  and 
  dorsally 
  from 
  the 
  promontorium. 
  

   The 
  fenestra 
  ovale 
  faces 
  slightly 
  forward 
  of 
  lateral 
  and 
  is 
  situ- 
  

   ated 
  very 
  deep 
  in 
  the 
  mesotympanic 
  fossa, 
  almost 
  directly 
  above 
  

   but 
  well 
  separated 
  from 
  the 
  promontorium. 
  It 
  is 
  much 
  higher 
  

   in 
  position 
  than 
  the 
  fenestra 
  rotunda 
  and 
  is 
  very 
  much 
  above 
  the 
  

   lip 
  of 
  the 
  trough 
  for 
  the 
  audital 
  tube. 
  Further 
  description 
  of 
  

   the 
  petrosal 
  and 
  its 
  relation 
  to 
  the 
  cranial 
  cavity 
  is 
  not 
  under- 
  

   taken, 
  inasmuch 
  as 
  such 
  additional 
  information 
  cannot 
  be 
  ob- 
  

   tained 
  without 
  damage 
  to 
  the 
  skull. 
  

  

  Upper 
  dentition. 
  — 
  The 
  dental 
  formula 
  for 
  the 
  upper 
  teeth 
  of 
  

   Maclmeroides 
  eothen 
  is 
  3-1-4-2, 
  as 
  noted 
  by 
  Matthew 
  in 
  Lim- 
  

   nocyon 
  and 
  as 
  observed 
  in 
  Thinocyon. 
  Moreover, 
  the 
  first 
  upper 
  

   molar 
  is 
  the 
  carnassial 
  as 
  in 
  these 
  forms 
  and 
  as 
  in 
  the 
  Oxyae- 
  

   nidae. 
  The 
  teeth 
  resemble 
  those 
  in 
  the 
  Limnocyoninae 
  with 
  

   certain 
  exceptional 
  characteristics 
  which 
  for 
  the 
  most 
  part 
  are 
  

   modifications 
  seemingly 
  accompanying 
  sabertooth 
  development. 
  

  

  The 
  incisors 
  are 
  slender, 
  recurved, 
  conical 
  teeth 
  adapted 
  for 
  

   piercing 
  and 
  with 
  transversely 
  fiattened 
  roots. 
  Unlike 
  Lim- 
  

   nocyon 
  they 
  increase 
  in 
  size 
  from 
  first 
  to 
  third, 
  P 
  being 
  much 
  

   more 
  robust 
  and 
  with 
  a 
  root 
  portion 
  about 
  twice 
  as 
  long 
  as 
  in 
  I'. 
  

   P 
  in 
  Limnocyon 
  is 
  much 
  smaller 
  than 
  P 
  and 
  may 
  not 
  be 
  present 
  

   in 
  some 
  individuals, 
  as 
  indicated 
  by 
  Matthew. 
  * 
  In 
  Thinocyon 
  

   the 
  three 
  are 
  subequal 
  and 
  slightly 
  spatulate. 
  

  

  The 
  enlarged 
  canine 
  is 
  preserved 
  only 
  on 
  the 
  left 
  side 
  and 
  is 
  

   broken 
  away 
  a 
  short 
  distance 
  below 
  the 
  alveolus. 
  It 
  is 
  removed 
  

   from 
  P 
  by 
  a 
  short 
  diastema. 
  The 
  tooth 
  as 
  exposed 
  has 
  no 
  cingu- 
  

   lum, 
  is 
  nearly 
  oval 
  in 
  cross 
  section, 
  and 
  has 
  a 
  long 
  gently 
  curved 
  

   root 
  section, 
  as 
  inferred 
  from 
  the 
  inflated 
  portion 
  of 
  the 
  maxilla. 
  

   In 
  Matthew's 
  ® 
  illustration 
  of 
  Limnocyon 
  verus 
  the 
  upper 
  canine 
  

   appears 
  to 
  have 
  an 
  exposed 
  cingulum 
  and 
  the 
  short 
  crown 
  is 
  

  

  • 
  Matthew, 
  W. 
  D., 
  ibid., 
  p. 
  434. 
  

   •Matthew, 
  W. 
  D., 
  ihid., 
  fig. 
  58. 
  

  

  