﻿A 
  STUDY 
  IN 
  CARCINOLOGY. 
  27 
  

  

  Oxystomata 
  into 
  a 
  division 
  (Abtheilung) 
  equal 
  in 
  value 
  to 
  the 
  Dromiidea 
  

   (Boas's 
  Dromiacea) 
  and 
  the 
  Brachyura, 
  the 
  last-named 
  division 
  including 
  all 
  

  

  other 
  true 
  crabs. 
  This 
  arrangement, 
  with 
  some 
  minor 
  modifications, 
  has 
  been 
  

   adopted 
  by 
  Alcock 
  (1, 
  1S96), 
  Borr/rdaile 
  (12, 
  1904), 
  and 
  Caiman 
  (23, 
  1909). 
  

   Against 
  these 
  authorities 
  must 
  be 
  set 
  the 
  opinion 
  of 
  A. 
  Milne 
  Edwards 
  and 
  

   Bouvier, 
  quoted 
  above, 
  and 
  the 
  similar 
  judgment 
  of 
  Boas 
  that 
  the 
  Raninidse 
  

   cannot 
  be 
  included 
  in 
  the 
  Oxystomata. 
  But 
  if 
  carcinologists 
  differ 
  as 
  to 
  (he 
  

   exact 
  position 
  that 
  the 
  Raninidse 
  should 
  occupy 
  among 
  the 
  crabs, 
  it 
  is 
  now 
  

   generally 
  agreed 
  (except 
  Ortmann 
  [42], 
  who 
  keeps 
  the 
  Oxystomata 
  apart 
  

   from 
  the 
  Brachyura) 
  that 
  they 
  are 
  true 
  crabs 
  belonging 
  to 
  the 
  section 
  

   Brachyura 
  and 
  not 
  to 
  the 
  section 
  Anomura 
  of 
  the 
  Decapoda 
  reptantia. 
  

   Indeed, 
  this 
  was 
  clearly 
  established 
  by 
  de 
  Haan 
  seventy 
  years 
  ago, 
  and 
  it 
  

   will 
  be 
  convenient 
  to 
  enumerate 
  here 
  the 
  Brachyuran 
  characters 
  of 
  the 
  

   Raninidse, 
  most 
  of 
  which 
  were 
  recognised 
  by 
  the 
  clear-sighted 
  author 
  of 
  the 
  

   volume 
  'Crustacea' 
  of 
  the 
  'Fauna 
  Japonica.' 
  They 
  are 
  : 
  — 
  (1) 
  The 
  reduced 
  

   abdomen 
  and 
  the 
  absence 
  of 
  uropods. 
  (2) 
  The 
  absence 
  of 
  pleopods 
  on 
  the 
  

   first 
  abdominal 
  somite 
  of 
  the 
  female. 
  (3) 
  The 
  absence 
  of 
  posterior 
  abdominal 
  

   appendages 
  in 
  the 
  male. 
  (4) 
  The 
  union 
  of 
  the 
  pterygostomial 
  region 
  of 
  the 
  

   carapace 
  with 
  the 
  epistome. 
  (5) 
  The 
  adherence 
  of 
  the 
  branchiostegite 
  to 
  

   the 
  thoracic 
  epimera. 
  (6) 
  The 
  reduction 
  of 
  the 
  branchiae. 
  (7) 
  The 
  absence 
  

   of 
  au 
  exopoditic 
  scale 
  on 
  the 
  second 
  antenna. 
  (8) 
  The 
  presence 
  of 
  a 
  sella 
  

   turcica 
  posterior. 
  (9) 
  The 
  expansion 
  of 
  the 
  ischium 
  and 
  merus 
  of 
  the 
  third 
  

   maxillipeds 
  to 
  form 
  a 
  plate-like 
  covering 
  to 
  the 
  other 
  mouth-parts. 
  (10) 
  The 
  

   presence 
  of 
  orbits 
  in 
  which 
  the 
  eye-stalks 
  can 
  be 
  concealed, 
  and 
  correlated 
  

   with 
  this 
  the 
  reduction 
  in 
  size 
  of 
  the 
  first 
  and 
  second 
  antenna?. 
  Other 
  

   characters 
  might 
  be 
  mentioned, 
  such 
  as 
  the 
  specialisation 
  of 
  the 
  thoracic 
  

   limbs 
  as 
  organs 
  of 
  locomotion, 
  involving 
  a 
  great 
  development 
  of 
  the 
  aj 
  o- 
  

   demes 
  forming 
  the 
  walls 
  of 
  the 
  cavities 
  in 
  which 
  the 
  muscles 
  of 
  the 
  limbs 
  are 
  

   contained. 
  In 
  other 
  words, 
  it 
  is 
  part 
  of 
  the 
  distinctive 
  facies 
  of 
  a 
  crab 
  that 
  

   the 
  musculature 
  is 
  highly 
  developed 
  in 
  connection 
  with 
  the 
  locomotory 
  

   thoracic 
  limbs, 
  and 
  is 
  feeble 
  almost 
  to 
  the 
  point 
  of 
  disappearance 
  in 
  (he 
  

   abdomen. 
  This 
  feature 
  is 
  strongly 
  marked 
  in 
  the 
  Raninidse. 
  

  

  On 
  the 
  other 
  hand, 
  it 
  is 
  generally 
  recognised 
  that 
  the 
  Raninidse 
  exhibit 
  a 
  

   number 
  of 
  Macruran 
  characters 
  which, 
  on 
  the 
  assumption 
  that 
  the 
  Brachyura 
  

   are 
  descended 
  from 
  the 
  Macrura, 
  are 
  primitive. 
  Among 
  the 
  more 
  important 
  

   of 
  these 
  are 
  : 
  — 
  The 
  comparatively 
  well-developed 
  rostrum, 
  which, 
  however, 
  is 
  

   absent 
  in 
  Cosmonotus. 
  The 
  proximal 
  segments 
  of 
  the 
  second 
  antenna 
  are 
  

   not 
  fused 
  with 
  the 
  epistome, 
  a 
  primitive 
  feature 
  also 
  shared 
  by 
  the 
  Dromiacea. 
  

   The 
  presence 
  of 
  a 
  sternal 
  canal 
  and 
  the 
  relatively 
  well-developed 
  anterior 
  

   thoracic 
  apodemes. 
  The 
  narrow 
  and 
  keel-like 
  posterior 
  thoracic 
  sternites. 
  

   The 
  oviducal 
  apertures 
  opening 
  on 
  the 
  eoxse 
  of 
  the 
  third 
  pereiopods, 
  another 
  

   primitive 
  character 
  shared 
  with 
  the 
  Dromiacea. 
  The 
  external 
  lobes 
  of 
  the 
  

  

  