﻿40 
  DR. 
  Q. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID.E 
  : 
  

  

  beyond 
  the 
  intersegmental 
  endopleurites 
  xiii/xiv, 
  unite 
  with 
  the 
  inner 
  edges 
  

   o£ 
  the 
  lower 
  part 
  of: 
  the 
  endopleurites 
  xii/xiii. 
  The 
  sella 
  turcica 
  of 
  Ranina 
  

   is 
  therefore 
  of 
  large 
  extent, 
  larger 
  than 
  in 
  so 
  typical 
  a 
  crab 
  as 
  Carcinus 
  

   mcenas. 
  Among 
  the 
  various 
  Brachyura 
  that 
  I 
  have 
  studied, 
  it 
  most 
  nearly 
  

   resembles 
  in 
  form 
  and 
  extent 
  that 
  of 
  Calappa. 
  But, 
  as 
  mentioned 
  above, 
  the 
  

   sella 
  turcica 
  is 
  not 
  found 
  in 
  all 
  crabs. 
  Fig. 
  15 
  represents 
  a 
  posterior 
  view 
  of 
  

   the 
  thorax 
  of 
  Dromia 
  vulgaris. 
  The 
  sterna 
  of 
  the 
  twelfth, 
  thirteenth, 
  and 
  

   fourteenth 
  segments 
  can 
  easily 
  be 
  recognised 
  by 
  the 
  strophidia 
  on 
  their 
  outer 
  

   extremities 
  ; 
  the 
  large 
  pair 
  of 
  ventro-lateral 
  projections 
  in 
  front 
  of 
  them 
  

   belong 
  to 
  the 
  eleventh 
  sternum 
  ; 
  their 
  strophidia, 
  being 
  on 
  their 
  anterior 
  

   face, 
  do 
  not 
  appear 
  in 
  the 
  drawing. 
  The 
  fourteenth 
  (last 
  thoracic) 
  sternum 
  

   does 
  not 
  differ 
  much 
  in 
  shape 
  from 
  that 
  of 
  Ranina 
  and 
  offers 
  resemblances 
  

   to 
  that 
  of 
  the 
  lobster. 
  The 
  thirteenth 
  and 
  twelfth 
  sterna 
  are 
  irregularly 
  

   shaped 
  transverse 
  bars, 
  of 
  which 
  the 
  outer 
  portions 
  are 
  calcified 
  and 
  

   distinctly 
  separated 
  by 
  apodemes, 
  but 
  their 
  admedian 
  portions 
  lose 
  their 
  

   distinctness 
  and 
  pass 
  into 
  a 
  median 
  membranous 
  pouch, 
  the 
  walls 
  of 
  which 
  

   are 
  little 
  if 
  at 
  all 
  calcified. 
  There 
  is 
  no 
  trace 
  of 
  a 
  median 
  longitudinal 
  

   apodeme 
  in 
  this 
  membranous 
  representative 
  of 
  the 
  penultimate 
  and 
  ante- 
  

   penultimate 
  thoracic 
  sterna, 
  consequently 
  there 
  is 
  no 
  sella 
  turcica. 
  The 
  

   arthrophragms 
  of 
  the 
  intersegment 
  xiv/xv 
  are 
  seen 
  converging 
  forward 
  from 
  

   the 
  anterior 
  edges 
  of 
  the 
  V-shaped 
  arms 
  of 
  the 
  last 
  thoracic 
  sternum, 
  and 
  in 
  

   oth^r 
  crabs 
  they 
  unite 
  above 
  with 
  the 
  epimera 
  of 
  their 
  own 
  segment, 
  in 
  front 
  

   with 
  the 
  arthrophragms 
  of 
  the 
  intersegment 
  in 
  front, 
  but 
  in 
  the 
  absence 
  of 
  

   the 
  ventral 
  apodeme 
  they 
  fall 
  far 
  short 
  of 
  meeting 
  in 
  the 
  middle 
  line 
  to 
  form 
  

   a 
  sella 
  turcica. 
  In 
  this 
  respect, 
  then, 
  Dromia 
  has 
  progressed 
  less 
  from 
  the 
  

   Macruran 
  towards 
  the 
  Brachyuran 
  condition 
  than 
  Ranina, 
  and 
  this 
  might 
  be 
  

   fastened 
  upon 
  as 
  an 
  argument 
  in 
  favour 
  of 
  the 
  derivation 
  of 
  the 
  Raninidas 
  as 
  

   of 
  all 
  other 
  crabs 
  from 
  a 
  Dromiaccan 
  ancestor, 
  but 
  the 
  transversely 
  elongated 
  

   twelfth 
  and 
  thirteenth 
  sterna 
  of 
  Dromia 
  are 
  quite 
  Brachyuran 
  in 
  character 
  

   and 
  very 
  different 
  from 
  the 
  narrow 
  and 
  keel-shaped 
  corresponding 
  sterna 
  

   in 
  the 
  Raninidse. 
  

  

  On 
  the 
  balance 
  the 
  evidence 
  afforded 
  by 
  the 
  structure 
  of 
  the 
  hinder 
  part 
  

   of 
  the 
  thorax 
  is 
  against 
  the 
  Dromiacean 
  ancestry 
  of 
  the 
  Raninida?. 
  

  

  Another 
  crab 
  in 
  which 
  the 
  sella 
  turcica 
  is 
  absent 
  is 
  Philyra 
  Uevis. 
  In 
  view 
  

   of 
  de 
  Haan's 
  emphatic 
  opinion 
  that 
  the 
  Leucosiida? 
  are 
  clearly 
  united 
  to 
  the 
  

   Raninidse 
  through 
  Lyreidus, 
  an 
  opinion 
  which 
  has 
  found 
  favour 
  with 
  subse- 
  

   quent 
  authors, 
  the 
  marked 
  differences 
  in 
  the 
  structure 
  of 
  the 
  thorax 
  demand 
  

   attention. 
  A 
  detailed 
  comparison 
  of 
  the 
  endophragmal 
  skeletons 
  of 
  the 
  

   Raninidse 
  and 
  Leucosiida? 
  is 
  best 
  reserved 
  for 
  the 
  discussion 
  of 
  the 
  possible 
  

   derivation 
  of 
  the 
  latter 
  from 
  the 
  former 
  family 
  in 
  another 
  part 
  of 
  the 
  paper, 
  

   but 
  it 
  may 
  lie 
  conveniently 
  pointed 
  out 
  in 
  this 
  place 
  that 
  in 
  Philyra 
  the 
  

   plastron 
  is 
  broadest 
  at 
  its 
  posterior 
  end 
  ; 
  the 
  intra-sternal 
  apodemes 
  are 
  nearly 
  

  

  