﻿A 
  STUDY 
  IN 
  CARCINOLOGY. 
  00 
  

  

  expanded, 
  and 
  modified 
  to 
  form 
  the 
  opercnliform 
  floor 
  of 
  the 
  exhalant 
  canal. 
  

   The 
  exopodite 
  is 
  somewhat 
  modified 
  and 
  to 
  a 
  varying 
  extent 
  in 
  different 
  

   genera, 
  but 
  it 
  is 
  always 
  shorter 
  than 
  the 
  endopodite, 
  does 
  not 
  share 
  in 
  the 
  

   formation 
  of 
  the 
  operculum, 
  on 
  the 
  whole 
  retains 
  the 
  characteristic 
  shape 
  of 
  

   an 
  exopodite, 
  and 
  invariably 
  hears 
  a 
  flagellum— 
  I 
  hope 
  I 
  may 
  not 
  he 
  criticised 
  

   for 
  attaching 
  undue 
  importance 
  to 
  a 
  trifling 
  character. 
  It 
  is 
  just 
  such 
  

   instances 
  as 
  this, 
  in 
  which 
  the 
  same 
  purpose 
  is 
  effected 
  by 
  somewhat 
  different 
  

   means, 
  that 
  afford 
  the 
  best 
  criteria 
  as 
  to 
  whether 
  some 
  particular 
  structural 
  

   resemblance 
  is 
  homogenetic 
  or 
  homoplastic. 
  It 
  was 
  the 
  discovery 
  of 
  tins 
  

   difference 
  in 
  the 
  structure 
  of 
  the 
  first 
  maxillipeds 
  that 
  finally 
  confirmed 
  my 
  

   opinion 
  that 
  the 
  Raninidse 
  are 
  not 
  genetically 
  connected 
  with 
  the 
  other 
  

   Oxystomatous 
  Crabs. 
  My 
  reliance 
  on 
  this 
  item 
  of 
  evidence 
  was 
  somewhat 
  

   shaken 
  by 
  A. 
  Milne 
  Edwards 
  and 
  Bouvier's 
  statement 
  that 
  the 
  opercular 
  

   floor 
  of 
  the 
  exhalant 
  canals 
  in 
  Cymonomus 
  is 
  formed 
  by 
  the 
  dilated 
  exopodites 
  

   of 
  the 
  first 
  maxilliped, 
  but 
  an 
  examination 
  of 
  their 
  figure 
  (28, 
  pi. 
  xv. 
  fig. 
  6— 
  

   there 
  is 
  a 
  mistake 
  in 
  the 
  numbering 
  of 
  these 
  figures—) 
  shows 
  that 
  the 
  

   resemblance 
  to 
  the 
  Raninidse 
  is 
  only 
  superficial, 
  and 
  the 
  exopodite 
  of 
  the 
  first 
  

   maxilliped 
  of 
  Cymonomus 
  has 
  a 
  long 
  six-jointed 
  flagellum 
  furnished 
  with 
  long 
  

   setse. 
  My 
  test 
  case, 
  therefore, 
  holds 
  good, 
  and 
  the 
  evidence 
  produced 
  is 
  

   sufficient 
  to 
  justify 
  Boas' 
  doubt 
  as 
  to 
  the 
  inclusion 
  of 
  the 
  Raninidse 
  among 
  

   the 
  other 
  Oxystomata, 
  and 
  A. 
  Milne 
  Edwards 
  and 
  Bouvier's 
  decision 
  to 
  

   exclude 
  them 
  from 
  their 
  monograph 
  on 
  the 
  Oxystomata 
  of 
  the 
  'Blake' 
  and 
  

   'Hassler 
  7 
  Expeditions. 
  The 
  Raninidse, 
  therefore, 
  must 
  be 
  removed 
  from 
  

   their 
  present 
  systematic 
  position 
  and 
  assigned 
  to 
  some 
  other 
  place 
  in 
  classi- 
  

   fication. 
  They 
  cannot 
  be 
  excluded 
  from 
  the 
  section 
  Brachyura 
  for 
  reasons 
  

   given 
  on 
  p. 
  27, 
  but 
  in 
  conformity 
  with 
  more 
  recent 
  and 
  generally 
  accepted 
  

   classifications 
  they 
  must 
  rank 
  as 
  a 
  separate 
  tribe, 
  equivalent 
  to 
  the 
  Dromiacea, 
  

   Brachygnatha, 
  and 
  the 
  rest 
  of 
  the 
  Oxystomata. 
  For 
  this 
  new 
  tribe 
  I 
  propose 
  

   the 
  name 
  Gymnopleura*, 
  which 
  directs 
  attention 
  to 
  one 
  of 
  the 
  most 
  charac- 
  

   teristic 
  features 
  of 
  the 
  group, 
  namely 
  the 
  exposure 
  of 
  the 
  epimera 
  of 
  the 
  

   posterior 
  thoracic 
  segments. 
  This 
  new 
  tribe 
  may 
  be 
  defined 
  as 
  follows. 
  

  

  Tribe 
  GYMNOPLEURA. 
  

  

  Anterior 
  thoracic 
  sterna 
  broad, 
  posterior 
  thoracic 
  sterna 
  narrow 
  and 
  keel- 
  

   like 
  ; 
  posterior 
  thoracic 
  epimera 
  largely 
  exposed 
  by 
  reduction 
  of 
  branchio- 
  

   stegi'te 
  : 
  female 
  openings 
  on 
  coxae 
  ; 
  last 
  pair 
  of 
  pereiopods 
  dorsal 
  in 
  position, 
  

  

  * 
  Mr 
  T. 
  R. 
  R. 
  Stebbing 
  in 
  'Nature, 
  1 
  Jany. 
  1922, 
  lias 
  pointed 
  out 
  that 
  Latreille 
  (Cours 
  

   d'Entomologie, 
  1831) 
  instituted 
  the 
  tribe 
  Notopterygia 
  for 
  Ranina. 
  At 
  first 
  sight 
  it 
  seemed 
  

   advisable 
  to 
  adopt 
  Latreille's 
  name 
  for 
  the 
  tribe 
  comprising 
  the 
  llaninidae 
  instead 
  ot 
  my 
  

   o.wn 
  But 
  the 
  rules 
  of 
  nomenclature 
  do 
  not 
  apply 
  to 
  tribal 
  names; 
  Latreille's 
  system 
  oi 
  

   classification 
  differs 
  largely 
  from 
  that 
  followed 
  in 
  this 
  paper 
  and 
  his 
  reasons 
  for 
  placing 
  

   Ranln,, 
  in 
  a 
  separate 
  tribe 
  differ 
  widely 
  from 
  mine. 
  Confusion 
  rather 
  than 
  perspicuity 
  

   would 
  result 
  from 
  the 
  adoption 
  of 
  Latreille's 
  tribal 
  name. 
  

  

  