﻿52 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINIDSE 
  : 
  

  

  palseontological 
  evidence 
  available, 
  as 
  far 
  as 
  it 
  goes, 
  supports 
  this 
  thesis. 
  

   The 
  Raninidse 
  are 
  ancient 
  forms 
  among 
  crabs, 
  and 
  when 
  they 
  make 
  their 
  

   first 
  appearance 
  have 
  their 
  characteristics 
  fully 
  developed. 
  The 
  earliest 
  

   fossils 
  of 
  which 
  I 
  can 
  find 
  a 
  sufficiently 
  exact 
  account 
  are 
  Raninella 
  Trigeri 
  

   from 
  the 
  ores 
  verts 
  of 
  Maine 
  (France) 
  and 
  R. 
  elongata 
  from 
  the 
  cretaceous 
  

   beds 
  of 
  the 
  Sarthe. 
  Both 
  deposits 
  belong 
  to 
  the 
  Turonian 
  division 
  of 
  the 
  

   Cretaceous. 
  In 
  these 
  early 
  Raninidse 
  the 
  carapace 
  is 
  of 
  elongated 
  oval 
  

   shape, 
  broadest 
  in 
  the 
  anterior 
  third 
  ; 
  the 
  " 
  buccal 
  frame 
  " 
  is 
  so 
  much 
  

   elongated 
  that 
  it 
  is 
  nearly 
  half 
  the 
  length 
  of 
  the 
  body 
  ; 
  the 
  thoracic 
  sterna, 
  

   wide 
  between 
  the 
  first 
  pair 
  of 
  legs, 
  become 
  narrowed 
  between 
  the 
  second 
  

   pair 
  and 
  are 
  reduced 
  to 
  linear 
  dimensions 
  between 
  the 
  posterior 
  pairs 
  of 
  

   pereiopods 
  ; 
  the 
  four 
  pairs 
  of 
  pereiopods 
  are 
  compressed 
  and 
  adapted 
  for 
  

   digging 
  in 
  sand 
  (A. 
  Milne 
  Edwards 
  27). 
  This 
  is 
  the 
  description 
  of 
  a 
  

   very 
  typical 
  Raninid 
  of 
  fossorial 
  habit 
  showing 
  no 
  greater 
  affinity 
  to 
  the 
  

   Prosoponidse 
  or 
  to 
  Protocarcinus 
  (Pcdadnachvs, 
  Woodw.) 
  than 
  do 
  existing 
  

   members 
  of 
  the 
  group. 
  The 
  presence 
  of 
  Ranina 
  marestiana 
  and 
  JS^otopus 
  

   Beyrichii 
  in 
  the 
  Eocene 
  show 
  that 
  modern 
  genera 
  of 
  the 
  Raninidse 
  were 
  then 
  

   differentiated 
  and 
  well 
  established. 
  Bittner's 
  (3) 
  excellent 
  figure 
  of 
  the 
  

   latter 
  species 
  might 
  pass 
  for 
  a 
  representation 
  of 
  the 
  anterior 
  half 
  of 
  the 
  cara- 
  

   pace 
  of 
  a 
  modern 
  Notopus. 
  Perhaps 
  the 
  geological 
  evidence 
  proves 
  no 
  more 
  

   than 
  the 
  antiquity 
  of 
  the 
  Raninidse, 
  but 
  that 
  antiquity 
  affords 
  support 
  to 
  

   the 
  argument 
  that 
  they 
  had 
  an 
  independent 
  origin 
  from 
  the 
  Astacura. 
  

  

  If, 
  then, 
  they 
  are 
  not 
  descended 
  from 
  aProtocarcinid-Prosoponid 
  stock 
  by 
  

   way 
  of 
  the 
  Dromiacea, 
  a 
  fortiori 
  the 
  Raninidse 
  cannot 
  be 
  descended 
  from 
  

   the 
  Dorippidse 
  or 
  Oyclodorippidse, 
  which 
  are 
  themselves 
  derived 
  from 
  the 
  

   Dromiacea. 
  From 
  what 
  has 
  preceded 
  it 
  is 
  evident 
  that 
  they 
  cannot 
  be 
  ; 
  

   their 
  primitive 
  nervous 
  system 
  and 
  endophragmal 
  skeleton 
  is 
  sufficient 
  

   evidence 
  of 
  that. 
  On 
  the 
  same 
  reasoning, 
  the 
  Dorippidse 
  cannot 
  be 
  descended 
  

   from 
  the 
  Raninidse, 
  for 
  it 
  has 
  been 
  shown 
  that 
  their 
  ancestry 
  is 
  altogether 
  

   different. 
  So 
  one 
  of 
  the 
  families, 
  and 
  that 
  the 
  most 
  primitive, 
  of 
  the 
  

   remainder 
  of 
  the 
  Oxystomata 
  is 
  excluded 
  from 
  relationship 
  with 
  the 
  

   Raninidse. 
  What, 
  then, 
  of 
  the 
  two 
  remaining 
  Oxystome 
  families, 
  the 
  

   Calappidre 
  and 
  the 
  Leucosiidse. 
  They 
  are 
  classified 
  with 
  the 
  Uaninidse 
  

   because 
  the 
  majority 
  of 
  carcinologists 
  have 
  found 
  it 
  difficult 
  to 
  believe 
  that 
  

   the 
  Oxystome 
  "mouth 
  frame" 
  could 
  have 
  been 
  acquired 
  independently 
  by 
  

   different 
  lines 
  of 
  descent. 
  But 
  since 
  the 
  Dorippidse 
  are 
  excluded 
  from 
  

   relationship 
  with 
  the 
  Raninidse 
  this 
  objection 
  no 
  longer 
  has 
  any 
  force. 
  But 
  

   there 
  is 
  room 
  for 
  the 
  opinion 
  that 
  the 
  Calappidse 
  and 
  Leucosiidse 
  are 
  

   descended 
  from 
  the 
  Raninidse, 
  and 
  I 
  have 
  already 
  quoted 
  (p. 
  26) 
  de 
  Haan's 
  

   positive 
  opinion 
  that 
  Lyreidus 
  is 
  an 
  annectant 
  form 
  with 
  the 
  Leucosiidse. 
  

   There 
  are, 
  of 
  course, 
  many 
  points 
  of 
  difference 
  between 
  the 
  Raninidse 
  and 
  

   the 
  two 
  above-named 
  families. 
  It 
  would 
  be 
  an 
  easy 
  though 
  a 
  lengthy 
  task 
  

  

  