﻿1864.] 
  DAWKINS 
  EHJSTIC 
  BEDS 
  AND 
  WHITE 
  LIAS. 
  411 
  

  

  and 
  worn 
  lower 
  premolar 
  of 
  Hypsiprymnus 
  Hunteri, 
  magnified 
  

   four 
  times, 
  the 
  latter 
  being 
  a 
  little 
  more 
  advanced 
  in 
  wear 
  than 
  

   the 
  fossil. 
  The 
  outer 
  and 
  lower 
  side 
  of 
  its 
  crown 
  presents 
  but 
  

   the 
  faintest 
  traces 
  of 
  the 
  plica?, 
  while 
  on 
  the 
  inside 
  they 
  are 
  easily 
  

   recognized. 
  It 
  proves 
  that 
  the 
  absence 
  of 
  plication 
  in 
  the 
  corre- 
  

   sponding 
  side 
  (the 
  lower) 
  of 
  the 
  fossil 
  cannot 
  be 
  admitted 
  as 
  evi- 
  

   dence 
  against 
  its 
  Hypsiprymnoid 
  character. 
  In 
  a 
  word, 
  the 
  nearest 
  

   living 
  representative 
  of 
  the 
  fossil 
  appears 
  to 
  me 
  to 
  be 
  Hypsiprymnus 
  

   Hunteri, 
  Bettongia 
  rufescens, 
  or 
  some 
  other 
  of 
  the 
  Kangaroo-rats 
  

   with 
  four-plicated 
  premolars. 
  All 
  the 
  premolars 
  of 
  Hypsiprymnus 
  

   which 
  I 
  have 
  examined 
  are 
  at 
  least 
  twice 
  the 
  size 
  of 
  the 
  fossil. 
  

  

  Figs. 
  3-5. 
  — 
  Ulustrating 
  the 
  affinities 
  of 
  Hypsiprymnopsis 
  

  

  Rhasticus. 
  

  

  Fig. 
  3. 
  

  

  Fig. 
  5. 
  

  

  Fig. 
  4 
  a. 
  

  

  Fig. 
  4 
  b. 
  

  

  Fig. 
  3. 
  Premolar 
  of 
  Hypsiprymnopsis 
  Bhceticus 
  ; 
  X 
  4. 
  

  

  4 
  b. 
  Right 
  lower 
  premolar 
  of 
  Hypsiprymnus 
  minor, 
  very 
  much 
  worn 
  ; 
  X 
  4 
  ; 
  

  

  = 
  H. 
  murinus 
  of 
  Hunt. 
  Cat. 
  1784. 
  

   4 
  a. 
  Unworn 
  left 
  lower 
  premolar 
  of 
  H. 
  minor 
  ; 
  X 
  4. 
  

   5. 
  Unworn 
  left 
  lower 
  premolar 
  of 
  H. 
  Hunteri 
  (Ow.) 
  ; 
  X 
  2. 
  

  

  Whether 
  or 
  not 
  the 
  tooth 
  belongs 
  to 
  the 
  Rhaetic 
  Mierolestes 
  cannot 
  

   be 
  decided, 
  because 
  the 
  tubercular 
  true 
  molars 
  of 
  the 
  latter 
  have 
  

   alone 
  been 
  found. 
  Nor 
  can 
  its 
  relation 
  to 
  Plagiaulax 
  be 
  affirmed, 
  

   as 
  the 
  worn 
  crown 
  reveals 
  nothing 
  of 
  the 
  verticality 
  or 
  the 
  obliquity 
  

   of 
  the 
  folds. 
  But, 
  nevertheless, 
  there 
  is 
  a 
  sufficiently 
  characteristic 
  

   portion 
  of 
  it 
  left 
  to 
  indicate 
  a 
  premolar 
  most 
  closely 
  allied 
  to 
  that 
  

   of 
  the 
  Kangaroo-rats. 
  Until, 
  therefore, 
  additional 
  remains 
  be 
  found, 
  

   I 
  have 
  provisionally 
  named 
  it 
  Hypsiprymnopsis 
  Bhceticus 
  — 
  a 
  name 
  

   that 
  represents 
  its 
  position 
  in 
  the 
  geological 
  scale 
  and 
  its 
  zoological 
  

   affinities. 
  

  

  § 
  V. 
  Range 
  of 
  Marsupials 
  in 
  Time. 
  

  

  It 
  is 
  a 
  very 
  significant 
  fact, 
  that 
  all 
  the 
  Secondary 
  Mammalia 
  that 
  

   have 
  with 
  any 
  accuracy 
  been 
  determined 
  represent 
  one 
  or 
  other 
  of 
  

   the 
  families 
  of 
  the 
  most 
  lowly 
  organized 
  Mammalian 
  order*. 
  Of 
  

  

  * 
  The 
  small 
  jaw 
  of 
  Sterecgnathus, 
  from 
  Stoncsfield, 
  is 
  sui 
  generis, 
  different 
  

  

  