﻿434 
  

  

  Mr. 
  O. 
  Thomas 
  on 
  a 
  new 
  Species 
  of 
  Mus. 
  

  

  outer 
  wall 
  of 
  infraorbital 
  foramen 
  evenly 
  convex, 
  not 
  over- 
  

   hanging 
  above, 
  or 
  hollowed 
  out 
  below. 
  Palatine 
  foramina 
  

   reaching 
  to 
  just 
  between 
  the 
  anterior 
  corners 
  of 
  the 
  first 
  

   molars. 
  Posterior 
  nares 
  broad, 
  the 
  spine 
  in 
  the 
  centre 
  of 
  the 
  

   posterior 
  edge 
  of 
  the 
  palate 
  unusually 
  well 
  developed. 
  Bulhe 
  

   small, 
  transparent. 
  

  

  Teeth. 
  — 
  Incisors 
  pale 
  orange 
  above, 
  yellow 
  below. 
  Upper 
  

   molars 
  (see 
  fig.) 
  very 
  narrow 
  and 
  elongated, 
  their 
  inner 
  cusps 
  

  

  Mus 
  argurus. 
  Upper 
  molar 
  teeth, 
  magnified 
  about 
  7 
  diameters. 
  

  

  all 
  along 
  unusually 
  well 
  developed, 
  while 
  their 
  outer 
  ones 
  are 
  

   almost 
  obsolete. 
  — 
  with 
  a 
  small 
  secondary 
  cusp 
  on 
  its 
  an- 
  

   terior 
  side, 
  exactly 
  as 
  in 
  the 
  Indian 
  Leggada 
  * 
  ; 
  laminae 
  three 
  

   in 
  number 
  as 
  usual, 
  but 
  the 
  external 
  cusps 
  on 
  these 
  laminae 
  

   extraordinarily 
  reduced, 
  obsolete 
  on 
  the 
  first 
  and 
  third 
  laminae, 
  

   and 
  nearly 
  so 
  on 
  the 
  second 
  ; 
  on 
  the 
  other 
  hand, 
  the 
  inner 
  

   cusps 
  are 
  very 
  large, 
  the 
  third 
  lamina 
  even, 
  which 
  generally 
  

   has 
  no 
  internal 
  cusp, 
  having 
  one 
  quite 
  as 
  large 
  as 
  the 
  others. 
  

   ^L? 
  with 
  two 
  laminae 
  as 
  usual, 
  each 
  of 
  which 
  has 
  its 
  small 
  

   internal 
  cusp, 
  in 
  addition 
  to 
  the 
  antero-internal 
  cusp 
  always 
  

   present 
  in 
  Mus, 
  there 
  being 
  therefore 
  three 
  internal 
  cusps 
  to 
  

   the 
  tooth 
  f. 
  — 
  , 
  j^Tl, 
  ^> 
  an 
  d 
  mTs 
  as 
  usual. 
  The 
  dentition 
  is 
  

  

  * 
  See 
  Proc. 
  Zool. 
  Soc. 
  1881, 
  p. 
  552, 
  pi. 
  li. 
  fig. 
  10. 
  

  

  t 
  This 
  fact 
  is 
  most 
  important, 
  as 
  it 
  seems 
  to 
  me 
  to 
  negative 
  Dr. 
  Winge's 
  

   suggestion 
  (" 
  Jordfuudne 
  og 
  Nulevende 
  Gnavera 
  fra 
  Lagoa 
  Santa," 
  E 
  

   Mus. 
  Lund. 
  iii. 
  p. 
  125, 
  1887) 
  that 
  the 
  ordinary 
  antero-internal 
  cusp 
  of 
  

   this 
  tooth 
  in 
  Mus 
  is 
  that 
  originally 
  belonging 
  to 
  the 
  first 
  lamina, 
  while 
  

   that 
  opposite 
  this 
  lamina 
  reilly 
  belongs 
  to 
  the 
  next 
  one, 
  the 
  two 
  having 
  

   been 
  pushed 
  out 
  of 
  their 
  normal 
  positions 
  by 
  the 
  increase 
  in 
  size 
  of 
  the 
  

  

  