﻿388 
  On 
  the 
  Species 
  o/Limnoria. 
  

  

  geographical 
  distribution, 
  and^ 
  in 
  tlie 
  case 
  of 
  Limnoria, 
  it 
  

   seems 
  possible 
  to 
  find 
  some 
  connection 
  between 
  the 
  species 
  

   and 
  their 
  distribution. 
  Thus 
  L. 
  segnis, 
  which 
  lias 
  probably 
  

   been 
  long 
  separated, 
  geographically, 
  from 
  the 
  other 
  species, 
  

   is 
  distinctly 
  marked 
  off 
  from 
  them 
  by 
  its 
  very 
  small 
  two- 
  

   jointed 
  mandible. 
  L. 
  lignontm, 
  which 
  is 
  found 
  in 
  the 
  north, 
  

   also 
  far 
  removed 
  from 
  most 
  of 
  the 
  other 
  species, 
  shows 
  dis- 
  

   tinct 
  differentiation 
  from 
  them 
  iu 
  the 
  small 
  size 
  of 
  the 
  epipod 
  

   of 
  the 
  maxillipeds; 
  oi 
  L.japonica 
  we 
  have 
  unfortunately 
  no 
  

   information 
  as 
  to 
  the 
  mouth-parts, 
  but 
  from 
  the 
  description 
  

   it 
  appears 
  that 
  it 
  is 
  closely 
  related 
  to 
  L. 
  lignorum, 
  differing 
  

   only 
  in 
  the 
  possession 
  of 
  tubercles 
  on 
  the 
  pleon, 
  and 
  it 
  may 
  

   be 
  anticipated 
  that 
  its 
  mandible 
  will 
  be 
  found 
  to 
  be 
  three- 
  

   jointed 
  and 
  the 
  epipods 
  of 
  the 
  maxillipeds 
  to 
  be 
  short; 
  it 
  

   comes 
  from 
  Japan, 
  not 
  so 
  very 
  far 
  from 
  the 
  Pacific 
  Coast 
  of 
  

   America, 
  from 
  which 
  L. 
  lignorum 
  has 
  been 
  recorded. 
  The 
  

   remaining 
  three 
  species 
  seem 
  more 
  closely 
  connected 
  with 
  

   one 
  another, 
  both 
  in 
  structure 
  and 
  in 
  distribution; 
  there 
  

   is 
  little 
  essential 
  difference 
  in 
  their 
  mouth-parts, 
  and 
  it 
  is 
  

   difficult 
  to 
  say 
  whether 
  they 
  can 
  continue 
  to 
  be 
  considered 
  as 
  

   distinct 
  species 
  when 
  forms 
  from 
  intermediate 
  localities 
  have 
  

   been 
  found. 
  L. 
  antarctica 
  appears 
  to 
  be 
  fairly 
  well 
  marked 
  

   off 
  from 
  the 
  other 
  two 
  ])y 
  the 
  small 
  size 
  of 
  both 
  rami 
  of 
  the 
  

   uropoda, 
  and 
  L. 
  andrewsi 
  may 
  be 
  distinguished 
  from 
  

   L. 
  pfefferi 
  by 
  the 
  shortness 
  of 
  the 
  peduncle 
  of 
  the 
  uropoda 
  ; 
  

   though 
  these 
  characters 
  are 
  proportional 
  only 
  and 
  may 
  

   perhaps 
  be 
  found 
  to 
  vary 
  with 
  the 
  age 
  of 
  the 
  specimen. 
  

  

  All 
  the 
  species, 
  except 
  L.segnis 
  and 
  L. 
  antarctica, 
  appear 
  

   to 
  be 
  wood-borers, 
  and 
  it 
  seems 
  likely 
  therefore 
  that 
  the 
  

   wood-boring 
  habit 
  is 
  characteristic 
  of 
  the 
  whole 
  genus 
  and 
  

   that 
  some 
  of 
  the 
  characters 
  of 
  the 
  animal, 
  such 
  as 
  the 
  small 
  

   size 
  of 
  the 
  body 
  and 
  the 
  shortness 
  of 
  the 
  antennae 
  and 
  the 
  

   perseopoda, 
  are 
  associated 
  with 
  the 
  wood-boring 
  habit. 
  The 
  

   wide 
  distribution 
  of 
  the 
  various 
  forms 
  and 
  their 
  small 
  amount 
  

   of 
  difference 
  may 
  therefore 
  bo 
  accounted 
  for 
  by 
  their 
  dis- 
  

   persal 
  by 
  means 
  of 
  floating 
  logs 
  into 
  which 
  they 
  were 
  boring 
  ; 
  

   if 
  this 
  is 
  so, 
  then 
  the 
  two 
  species 
  which 
  are 
  not 
  now 
  wood- 
  

   borers 
  must 
  have 
  lost 
  the 
  wood-boring 
  habit 
  through 
  being 
  

   cast 
  on 
  some 
  shore 
  where 
  wood 
  for 
  boring 
  was 
  not 
  available, 
  

   and 
  having 
  had 
  to 
  adapt 
  themselves 
  to 
  another 
  mode 
  of 
  life. 
  

   It 
  is 
  possible 
  that 
  this 
  occurred 
  on 
  the 
  Antarctic 
  Continent, 
  

   and 
  that 
  L. 
  segnis 
  has 
  reached 
  New 
  Zealand 
  by 
  way 
  of 
  the 
  

   Antarctic 
  Continent, 
  and 
  in 
  doing 
  so 
  has 
  had 
  the 
  mandibular 
  

   palp 
  more 
  reduced 
  than 
  it 
  is 
  in 
  L. 
  antarctica 
  (the 
  sj^ecies 
  to 
  

   which 
  it 
  is 
  probably 
  most 
  nearly 
  allied) 
  and 
  in 
  the 
  species 
  

   livino- 
  in 
  the 
  Indian 
  Ocean. 
  

  

  