﻿some 
  Remains 
  of 
  Rodents. 
  187 
  

  

  inner 
  folds 
  of 
  ^n! 
  <^ie 
  out 
  on 
  the 
  sides 
  of 
  the 
  teeth 
  a 
  little 
  below 
  

   the 
  present 
  grinding-surt'ace, 
  so 
  that, 
  with 
  a 
  little 
  further 
  wear, 
  

   these 
  folds 
  would 
  be 
  converted 
  into 
  enamel 
  " 
  islets." 
  ^4 
  is 
  

   in 
  relation 
  to 
  ^^ 
  a 
  little 
  longer 
  antero-posteriorly 
  than 
  in 
  

   C. 
  fiber; 
  its 
  anterior 
  surface 
  is 
  lightly 
  furrowed 
  by 
  a 
  weak 
  

   vertical 
  sulcus 
  — 
  the 
  last 
  trace 
  of 
  a 
  former 
  more 
  complex 
  

   condition 
  of 
  the 
  anterior 
  loop. 
  

   Dimensions 
  : 
  — 
  

  

  C, 
  veterior, 
  C 
  fiber. 
  

  

  mm. 
  mm. 
  

  

  Antero-posterior 
  length 
  of 
  jTl 
  10 
  9-5 
  

  

  Width 
  of 
  ,74 
  behind 
  8 
  8 
  

  

  Antero-posterior 
  length 
  of 
  ^^\ 
  7 
  8'5 
  

  

  In 
  the 
  two 
  upper 
  premolars, 
  from 
  tiie 
  Red 
  Crag 
  of 
  Sutton, 
  

   upon 
  which 
  Sir 
  E. 
  Eay 
  Lankester 
  based 
  his 
  C. 
  veterior^, 
  

   Mr. 
  E. 
  T. 
  Newton 
  found 
  that 
  ''two 
  of 
  tiie 
  three 
  outer 
  folds 
  

   of 
  enamel 
  are 
  only 
  open 
  to 
  the 
  exterior 
  for 
  a 
  short 
  distance 
  

   from 
  the 
  summit 
  of 
  the 
  tooth"t; 
  the 
  lower 
  teeth 
  now 
  

   described 
  present 
  corresponding 
  characters, 
  and 
  may 
  there- 
  

   fore 
  be 
  referred 
  to 
  C. 
  veterior. 
  Tiie 
  differences 
  in 
  the 
  number 
  

   of 
  folds 
  reduced 
  peripherally 
  in 
  the 
  individual 
  teeth, 
  viz., 
  all 
  

   three 
  inner 
  in 
  ^7J, 
  two 
  outer 
  in 
  ^, 
  and 
  one 
  inner 
  in 
  ^^74, 
  are 
  in 
  

   harmony 
  with 
  our 
  experience 
  of 
  such 
  reductions 
  in 
  other 
  

   rodents. 
  

  

  In 
  the 
  relatively 
  large 
  size 
  of 
  ^, 
  and 
  in 
  the 
  early 
  conversion 
  

   into 
  "islets" 
  of 
  the 
  inner 
  folds 
  of 
  lower 
  and 
  the 
  outer 
  folds 
  

   of 
  upper 
  cheek-teeth, 
  C. 
  veterior 
  makes 
  some 
  approach 
  den- 
  

   tally 
  towards 
  Trogontherium 
  ; 
  in 
  the 
  latter 
  all 
  the 
  enamel 
  

   folds 
  are 
  so 
  reduced 
  during 
  wear, 
  and 
  in 
  its 
  later 
  species 
  there 
  

   is 
  a 
  great 
  increase 
  in 
  the 
  size 
  of 
  the 
  animal. 
  

  

  C. 
  issiodorensisj 
  Croizet, 
  is 
  stated 
  by 
  Pomel 
  J, 
  Gervais§, 
  

   and 
  Bosco 
  || 
  to 
  be 
  hardly 
  or 
  not 
  at 
  all 
  different 
  from 
  C. 
  fiber, 
  

   so 
  far 
  as 
  it 
  is 
  known. 
  C. 
  prcefihtr, 
  Deperet^, 
  from 
  the 
  

   Pliocene 
  of 
  Housillon, 
  is 
  distinguished 
  by 
  its 
  slender 
  molars 
  

   and 
  the 
  absence 
  of 
  a 
  third 
  trochanter 
  to 
  the 
  femur. 
  To 
  one 
  

   of 
  these 
  two 
  forms 
  the 
  Hed 
  Crag 
  beaver 
  with 
  persistent 
  

   enamel-folds, 
  provisionally 
  referred 
  by 
  Newton 
  to 
  C 
  fiber^ 
  

   not 
  improbably 
  belongs, 
  

  

  * 
  Lankester, 
  Ann. 
  & 
  Mag. 
  Nat. 
  Hist.(3) 
  xiv. 
  p. 
  355 
  (1864). 
  

   t 
  Newton, 
  ' 
  Vertebrata 
  of 
  the 
  Pliocene 
  Deposits 
  of 
  Britain/ 
  p. 
  50 
  

   (1891). 
  

  

  X 
  Pomel, 
  ' 
  Catalogue 
  Methodique,' 
  p. 
  20, 
  

  

  § 
  Gervais, 
  Zool. 
  et 
  Pal. 
  Fran^. 
  1859, 
  p. 
  20. 
  

  

  II 
  Bosco, 
  ' 
  Palseontographia 
  Italica,' 
  v. 
  p. 
  89. 
  

  

  ii 
  Deperet, 
  Mem. 
  See. 
  Geol. 
  de 
  France, 
  Paleontol. 
  no. 
  3 
  (1890). 
  

  

  