﻿246 
  THE 
  ZOOLOGIST. 
  

  

  came 
  to 
  exist 
  in 
  this 
  small 
  group 
  of 
  islands 
  whilst 
  the 
  species 
  is 
  

   totally 
  absent 
  from 
  the 
  Shetland's, 
  and 
  very 
  different 
  from 
  that 
  

   found 
  in 
  Scotland, 
  only 
  about 
  twenty 
  miles 
  away, 
  one 
  must 
  yet 
  

   notice 
  two 
  curious 
  zoological 
  points. 
  First, 
  we 
  are 
  at 
  once 
  

   struck 
  by 
  the 
  fact, 
  instanced 
  both 
  in 
  this 
  case 
  and 
  that 
  of 
  the 
  

   recently 
  described 
  Skomer 
  (Bank) 
  Yole, 
  that 
  here 
  we 
  have 
  two 
  

   boreal 
  mammals, 
  living 
  in 
  a 
  small 
  isolated 
  island 
  or 
  islands 
  

   situated 
  close 
  to 
  a 
  large 
  island 
  (Great 
  Britain), 
  and 
  presenting 
  

   in 
  both 
  cases 
  much 
  larger 
  forms 
  than 
  the 
  type 
  living 
  on 
  the 
  big 
  

   island 
  or 
  continent, 
  such 
  as 
  it 
  must 
  have 
  been 
  prior 
  to 
  the 
  

   second 
  insulation. 
  Students 
  of 
  zoology 
  are 
  well 
  aware 
  that, 
  

   almost 
  without 
  exception, 
  types 
  found 
  on 
  islands 
  similar 
  in 
  all 
  

   respects 
  to 
  those 
  on 
  the 
  mainland 
  are 
  almost 
  invariably 
  smaller. 
  

   Secondly, 
  I 
  would 
  point 
  out 
  that 
  the 
  depth 
  of 
  the 
  Pentland 
  Firth 
  

   is 
  great, 
  and 
  its 
  tideway 
  one 
  of 
  the 
  strongest 
  in 
  the 
  world 
  ; 
  so 
  

   it 
  is 
  reasonable 
  to 
  suppose 
  that 
  the 
  Orkneys 
  were 
  separated 
  

   from 
  Great 
  Britain 
  long 
  before 
  that 
  country 
  became 
  an 
  island, 
  

   and 
  were 
  then 
  possibly 
  a 
  promontory 
  of 
  Scandinavia. 
  Why 
  no 
  

   boreal 
  Vole 
  is 
  found 
  in 
  the 
  Shetlands 
  I 
  cannot 
  understand, 
  but 
  

   close 
  search 
  may 
  yet 
  discover 
  it. 
  

  

  [At 
  Mr. 
  Millais's 
  request, 
  I 
  have 
  examined 
  the 
  specimens 
  of 
  

   Microtus 
  orcadensis, 
  and 
  may 
  say 
  at 
  once 
  that 
  it 
  is 
  a 
  most 
  distinct 
  

   species, 
  and 
  one 
  of 
  the 
  most 
  interesting 
  and 
  unexpected 
  dis- 
  

   coveries 
  ever 
  made 
  in 
  British 
  mammolog} 
  7 
  . 
  The 
  exact 
  relation- 
  

   ships 
  of 
  M. 
  orcadensis 
  are 
  by 
  no 
  means 
  clear, 
  and 
  will 
  need 
  to 
  be 
  

   studied 
  with 
  a 
  full 
  knowledge 
  of 
  the 
  continental 
  species 
  of 
  the 
  

   genus. 
  From 
  M. 
  agrestis 
  it 
  differs 
  not 
  only 
  by 
  the 
  characters 
  

   pointed 
  out 
  by 
  Mr. 
  Millais, 
  but 
  by 
  not 
  possessing 
  any 
  trace 
  of 
  the 
  

   fifth 
  triangle 
  to 
  the 
  second 
  upper 
  molar 
  so 
  characteristic 
  of 
  that 
  

   species, 
  while 
  its 
  skull 
  is 
  also 
  peculiar 
  both 
  in 
  shape 
  and 
  size. 
  

   Yet 
  it 
  does 
  not 
  seem 
  related 
  either 
  to 
  the 
  M. 
  ratticejjs 
  or 
  M. 
  

   arvalis 
  group. 
  This 
  animal 
  thus 
  presents 
  a 
  most 
  interesting 
  

   problem, 
  both 
  zoological 
  and 
  geographical.— 
  Oldfield 
  Thomas. 
  J 
  

  

  