﻿A 
  STUDY 
  IN 
  CARCINOLOGY. 
  47 
  

  

  mandible, 
  thus 
  forming 
  the 
  hinge-line 
  about 
  which 
  the 
  mandible 
  rotates. 
  

   The 
  postero-external 
  edge 
  of 
  the 
  plate 
  is 
  ill-defined 
  and 
  passes 
  into 
  an 
  

   imperfectly 
  calcified 
  area 
  forming 
  the 
  roof 
  of 
  the 
  branchial 
  canal. 
  The 
  

   membrane 
  narrows 
  posteriori}', 
  and 
  arriving 
  at 
  the 
  external 
  articular 
  pro- 
  

   cess 
  of 
  the 
  mandible, 
  again 
  becomes 
  calcified 
  and 
  thickened 
  to 
  form 
  a 
  rather 
  

   large 
  strophidiuin 
  for 
  articulation 
  with 
  the 
  mandible. 
  After 
  comparison 
  

   with 
  many 
  other 
  species, 
  I 
  have 
  satisfied 
  myself 
  that 
  the 
  whole 
  of 
  this 
  area, 
  

   calcified 
  in 
  front 
  and 
  behind, 
  but 
  imperfectly 
  calcified 
  or 
  membranous 
  in 
  

   the 
  middle, 
  represents 
  the 
  epimeron 
  of 
  the 
  mandibular 
  segment, 
  which 
  

   in 
  the 
  Astacura 
  is 
  fused 
  to 
  the 
  antennary 
  epimeron, 
  but 
  in 
  some 
  primitive 
  

   Brachyura, 
  as 
  I 
  shall 
  show 
  subsequently, 
  is 
  quite 
  independent 
  of 
  it 
  and 
  

   also 
  of 
  the 
  antennary 
  sternum. 
  Relying 
  on 
  these 
  interpretations 
  which, 
  I 
  

   venture 
  to 
  think, 
  will 
  be 
  accepted 
  by 
  anyone 
  who 
  makes 
  a 
  careful 
  compara- 
  

   tive 
  study 
  of 
  this 
  region, 
  I 
  shall 
  henceforth 
  discard 
  the 
  misleading 
  and 
  

   purely 
  topographical 
  names 
  in 
  general 
  use 
  and 
  speak 
  of 
  the 
  sterna, 
  epimera, 
  

   etc., 
  of 
  the 
  various 
  segments. 
  

  

  Before 
  bringing 
  the 
  Raninidse 
  into 
  comparison 
  it 
  will 
  be 
  well 
  to 
  consider 
  

   the 
  characters 
  presented 
  by 
  some 
  other 
  Oxystome 
  crabs, 
  particularly 
  of 
  

   the 
  Dorippidpe 
  from 
  which, 
  according 
  to 
  some 
  authors, 
  the 
  Raninidse 
  are 
  

   I 
  descended. 
  I 
  have 
  studied 
  Dorippe 
  lunata, 
  M. 
  Edw., 
  sEtlntsa 
  ciliatifrons, 
  

   ml 
  Fax., 
  and 
  jEilvusina 
  gracilipes, 
  ^iers. 
  Of 
  these 
  the 
  last-named 
  species 
  

   shows 
  the 
  most 
  primitive 
  and 
  interesting 
  features, 
  and 
  its 
  mouth-frame 
  and 
  

   antennary 
  region 
  are 
  depicted 
  in 
  fig. 
  21. 
  The 
  basal 
  joints 
  of 
  the 
  anfcennules 
  

   are 
  enormously 
  inflated 
  and 
  interposed 
  between 
  the 
  exposed 
  portions 
  of 
  the 
  

   ocular 
  peduncles 
  and 
  the 
  rostrum. 
  The 
  antennas 
  have 
  a 
  four-jointed 
  peduncle 
  

   and 
  a 
  fairly 
  long 
  flagellum 
  ; 
  the 
  basal 
  joint 
  is 
  small 
  but 
  freely 
  moveable. 
  

   The 
  downward 
  process 
  of 
  the 
  front 
  or 
  rostrum 
  articulates 
  with 
  the 
  antennulary 
  

   sternum, 
  the 
  latter 
  being 
  produced 
  right 
  and 
  left 
  into 
  wings 
  which 
  are 
  

   adapted 
  to 
  the 
  shape 
  of 
  the 
  inflated 
  basal 
  joints 
  of 
  the 
  antennules. 
  In 
  this 
  

   species 
  the 
  antennulary 
  sternum 
  is 
  largely 
  exposed, 
  only 
  its 
  posterior 
  margin 
  

   is 
  overlapped 
  by 
  the 
  front 
  end 
  of 
  the 
  spout-shaped 
  antennary 
  sternum. 
  

   The 
  latter 
  sclerite 
  is 
  well 
  defined 
  and 
  the 
  sutures 
  uuiting 
  it 
  to 
  adjacent 
  

   parts 
  can 
  be 
  seen 
  clearly. 
  It 
  consists 
  of 
  a 
  central 
  somewhat 
  scutiform 
  plate 
  

   with 
  antero-external 
  projections 
  of 
  which 
  the 
  edges 
  are 
  inrolled 
  ventrallv 
  to 
  

   form 
  the 
  spout-shaped 
  Oxystomatous 
  mouth. 
  It 
  is 
  to 
  the 
  hinder 
  ends 
  of 
  

   these 
  lateral 
  infolded 
  projections 
  that 
  the 
  pterygostomial 
  processes 
  of 
  the 
  

   carapace 
  are 
  united. 
  Behind 
  the 
  body 
  of 
  the 
  antennary 
  sternum 
  is 
  the. 
  

   mandibular 
  sternum, 
  a 
  very 
  slender 
  but 
  distinct 
  and 
  calcified 
  curved 
  bar. 
  

   Right 
  and 
  left, 
  intervening 
  between 
  the 
  lateral 
  wings 
  of 
  the 
  antennary 
  

   sternum 
  and 
  the 
  outer 
  ends 
  of 
  the 
  mandibular 
  sternum, 
  are 
  two 
  distinctly 
  

   defined 
  oval 
  plates 
  forming 
  the 
  roof 
  of 
  the 
  anterior 
  part 
  o£ 
  the 
  branchial 
  canal 
  

   and 
  extending 
  so 
  far 
  backward 
  that 
  they 
  supply 
  the 
  articular 
  strophingia 
  for 
  

  

  