﻿54 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID.E 
  : 
  

  

  relationship 
  with 
  the 
  Raninidse. 
  De 
  Haan 
  laid 
  great 
  stress 
  on 
  this 
  point 
  of 
  

   resemblance 
  between 
  the 
  Loucosiidseand 
  the 
  Raninidse, 
  but 
  a 
  detail 
  examina- 
  

   tion 
  shows 
  that 
  the 
  result 
  is 
  arrived 
  at 
  in 
  a 
  different 
  manner 
  in 
  the 
  two 
  

   families 
  and 
  must 
  be 
  regarded 
  as 
  a 
  case 
  of 
  homoplasy 
  rather 
  than 
  homogeny. 
  

   In 
  all 
  the 
  Raninidse 
  the 
  free 
  end 
  of 
  the 
  sternal 
  plastron 
  is 
  formed 
  by 
  the 
  

   more 
  or 
  less 
  prominent 
  lanceolate 
  median 
  projection 
  of 
  the 
  tenth 
  (chelipedal) 
  

   sternum. 
  The 
  ninth 
  sternum 
  is 
  narrow 
  and 
  projects 
  upwards 
  at 
  an 
  angle 
  

   of 
  130° 
  to 
  135° 
  above 
  the 
  lanceolate 
  projection 
  of 
  the 
  tenth 
  sternum. 
  The 
  

   coxpe 
  of 
  the 
  third 
  maxillipeds 
  are 
  articulated 
  to 
  the 
  hinder 
  end 
  of 
  the 
  narrow 
  

   ninth 
  sternum, 
  and 
  therefore 
  close 
  to 
  the 
  median 
  line, 
  and 
  they 
  effectively 
  

   exclude 
  any 
  part 
  of 
  the 
  sternum 
  from 
  participation 
  in 
  the 
  formation 
  of 
  the 
  

   broad 
  plastron 
  (see 
  fig. 
  27, 
  ix). 
  Further, 
  in 
  the 
  Raninidse, 
  the 
  connection 
  

   between 
  branchiostegite 
  and 
  plastron 
  in 
  front 
  of 
  the 
  cheliped 
  is 
  effected 
  by 
  

   lateral 
  outgrowths 
  of 
  the 
  tenth 
  sternum 
  which 
  meet 
  the 
  branchiostegal 
  

   margin, 
  not 
  by 
  any 
  marked 
  ingrowths 
  of 
  the 
  latter. 
  In 
  the 
  Leucosiidse 
  

   (I 
  have 
  studied 
  the 
  arrangement 
  in 
  Ilia 
  nucleus, 
  Ph'dyxia 
  undecimspinosa, 
  

   and 
  Philyra 
  Icevis) 
  the 
  ninth 
  sternum 
  is 
  short 
  antero-posteriorly, 
  but 
  broad 
  

   and 
  forms 
  the 
  anterior 
  end 
  of 
  the 
  plastron. 
  The 
  coxae 
  of 
  the 
  third 
  maxilli- 
  

   peds 
  are 
  articulated 
  to 
  its 
  outer 
  ends 
  and 
  are 
  therefore 
  far 
  apart. 
  The 
  tenth 
  

   sternum 
  does 
  not 
  give 
  off 
  any 
  prominent 
  outgrowths 
  in 
  front 
  of 
  the 
  chelipeds, 
  

   but 
  is 
  united 
  to 
  an 
  inwardly 
  directed 
  process 
  of 
  the 
  edge 
  of 
  the 
  branchio- 
  

   stegite 
  on 
  each 
  side, 
  this 
  process 
  being 
  the 
  most 
  anterior 
  of 
  a 
  series 
  of 
  

   similar 
  downgrowth's 
  of 
  the 
  branchiostegal 
  margin 
  which 
  pass 
  between 
  the 
  

   coxpe 
  of 
  the 
  pereipods 
  and 
  effect 
  the 
  very 
  close 
  and 
  elaborate 
  fit 
  of 
  branchio- 
  

   stegite 
  to 
  cox;e 
  already 
  referred 
  to. 
  It 
  may 
  be 
  mentioned 
  here 
  that 
  

   A. 
  Milne 
  Edwards 
  and 
  Bouvier 
  (28) 
  have 
  described 
  a 
  shallow 
  pterygostomial 
  

   gutter 
  closed 
  in 
  below 
  by 
  the 
  third 
  maxillipeds 
  in 
  Cyclodorippe. 
  This 
  

   gutter 
  occupies 
  the 
  same 
  position 
  as 
  the 
  well-known 
  pterygostomial 
  inhalant 
  

   canal 
  of 
  the 
  Leucosiidse, 
  and 
  the 
  similarity 
  of 
  the 
  structural 
  appointments 
  is 
  

   so 
  great 
  as 
  to 
  suggest 
  the 
  derivation 
  of 
  the 
  Leucosiidse 
  from 
  a 
  Cyclodorippid 
  

   rather 
  than 
  from 
  a 
  Raninid 
  ancestor. 
  

  

  Finally 
  some 
  importance 
  is 
  to 
  be 
  attached 
  to 
  an 
  apparently 
  minor 
  feature. 
  

   In 
  all 
  the 
  Oxystomatous 
  Crabs 
  the 
  floor 
  of 
  the 
  exhalant 
  branchial 
  canal 
  is 
  

   formed 
  by 
  an 
  expanded 
  spoon-shaped 
  operculum 
  furnished 
  by 
  the 
  first 
  

   maxilliped. 
  In 
  the 
  Raninidse 
  (see 
  figs. 
  31, 
  45, 
  50, 
  & 
  53) 
  both 
  the 
  exopodite 
  

   and 
  endopodite 
  are 
  expanded 
  and 
  modified, 
  and 
  co-operate 
  in 
  forming 
  the 
  

   operculiform 
  floor 
  in 
  question, 
  but 
  it 
  is 
  the 
  exopodite 
  which 
  is 
  the 
  longest, 
  

   most 
  expanded, 
  and 
  the 
  most 
  effective 
  agent 
  in 
  forming 
  the 
  operculiform 
  

   floor 
  of 
  the 
  anterior 
  part 
  of 
  the 
  exhalant 
  canal. 
  This 
  modified 
  exopodite 
  

   never 
  bears 
  a 
  flagellum. 
  In 
  the 
  Leucosiidse, 
  the 
  Calappinse, 
  and 
  the 
  

   Matutinse 
  (Grarstang 
  is 
  in 
  error 
  in 
  stating 
  that 
  the 
  exopodite 
  is 
  operculiform 
  

   in 
  Matuta 
  banksii) 
  it 
  is 
  the 
  endopodite 
  of 
  the 
  first 
  maxilliped 
  that 
  is 
  elongated. 
  

  

  