﻿50 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID.E 
  : 
  

  

  but 
  it 
  is 
  so 
  intimately 
  fused 
  to 
  the 
  antennary 
  sternum 
  that 
  no 
  suture 
  is 
  

   visible. 
  

  

  Posteriorly 
  the 
  mandibular 
  epimeron 
  is 
  continued 
  into 
  the 
  flexible 
  mem- 
  

   brane 
  forming 
  the 
  roof 
  and 
  outer 
  wall 
  of 
  the 
  branchial 
  canal. 
  In 
  Notosceles 
  

   (fig. 
  24) 
  the 
  antennary 
  sternum 
  is 
  very 
  short, 
  is 
  easily 
  separable 
  from 
  

   the 
  antennulary 
  sternum, 
  and 
  the 
  intersegmental 
  arthophrragm 
  iii/iv 
  in 
  

   front, 
  and 
  the 
  mandibular 
  epimera 
  appear 
  to 
  be 
  wholly 
  membranous. 
  In 
  

   Lyreidus, 
  on 
  the 
  other 
  hand 
  (fig. 
  25), 
  in 
  keeping 
  with 
  the 
  great 
  elongation 
  

   of 
  the 
  p 
  re-oral 
  region 
  of 
  the 
  carapace, 
  the 
  anterior 
  part 
  of 
  the 
  antennary 
  

   sternum 
  is 
  greatly 
  produced 
  and 
  to 
  a 
  certain 
  extent 
  overlaps, 
  but 
  does 
  not 
  

   conceal, 
  the 
  antennulary 
  sternum. 
  The 
  regions 
  of 
  the 
  mandibular 
  epimera 
  

   are 
  also 
  produced 
  far 
  backwards 
  on 
  either 
  side 
  of 
  the 
  mandibular 
  sternum 
  

   and 
  are 
  calcified, 
  but 
  I 
  cannot 
  find 
  any 
  line 
  of 
  division 
  between 
  them 
  and 
  

   the 
  antennary 
  sternum. 
  It 
  should 
  be 
  observed 
  that 
  in 
  Lyreidus 
  the 
  pterygo- 
  

   stomial 
  lobes 
  of 
  the 
  carapace 
  are 
  produced 
  far 
  in 
  front 
  of 
  the 
  mandibles 
  

   and 
  are 
  united 
  for 
  a 
  considerable 
  distance 
  with 
  the 
  edges 
  of 
  the 
  antennary 
  

   sternum, 
  a 
  condition 
  very 
  different 
  from 
  that 
  in 
  the 
  Leucosiidaa, 
  with 
  which 
  

   Lyreidus 
  has 
  so 
  often 
  been 
  compared. 
  

  

  From 
  what 
  precedes 
  it 
  is 
  evident 
  that 
  the 
  Raninidae 
  diverge 
  so 
  much 
  from 
  

   the 
  Dorippidse 
  and 
  are 
  so 
  much 
  more 
  primitive 
  in 
  several 
  important 
  par- 
  

   ticulars, 
  that 
  they 
  cannot 
  be 
  descended 
  from 
  the 
  latter 
  family. 
  Nor 
  does 
  a 
  

   comparison 
  of 
  the 
  pre-oral 
  segments 
  give 
  any 
  support 
  to 
  the 
  descent 
  of 
  the 
  

   Raninidpe 
  from 
  the 
  Dromiacea. 
  Fig. 
  27 
  is 
  a 
  frontal 
  view 
  of 
  the 
  antennary 
  

   and 
  oral 
  regions 
  of 
  Dromia 
  vulgaris. 
  The 
  antenna? 
  and 
  antennules 
  have 
  

   been 
  removed 
  and 
  also 
  the 
  left 
  ocular 
  peduncle, 
  but 
  that 
  of 
  the 
  right 
  side 
  is 
  

   left 
  in 
  place. 
  The 
  whole 
  facies 
  is 
  more 
  cancroid 
  than 
  in 
  the 
  Raninida?. 
  The 
  

   proximal 
  ends 
  of 
  the 
  ocular 
  peduncles, 
  concealed 
  behind 
  the 
  inflated 
  basal 
  

   joints 
  of 
  the 
  antennules 
  when 
  the 
  latter 
  are 
  in 
  place, 
  are 
  membranous. 
  The 
  

   antennulary 
  and 
  antennary 
  fossae 
  are 
  small 
  and 
  lie 
  in 
  nearly 
  the 
  same 
  trans- 
  

   verse 
  line. 
  The 
  orbits 
  so 
  far 
  resemble 
  those 
  of 
  the 
  Raninidae 
  that 
  there 
  are 
  

   no 
  downward 
  processes 
  of 
  the 
  front 
  external 
  to 
  the 
  antennules. 
  The 
  median 
  

   triangular 
  shield 
  with 
  the 
  apex 
  directed 
  forward 
  is 
  the 
  anteunular 
  sternum, 
  

   and 
  evidently 
  is 
  what 
  Milne 
  Edwards 
  called 
  the 
  " 
  epistome 
  " 
  (Joe. 
  cit.). 
  It 
  

   is 
  separated 
  by 
  a 
  distinct 
  but 
  shallow 
  membranous 
  apodeme 
  from 
  the 
  

   antennary 
  sternum 
  behind, 
  and 
  there 
  is 
  a 
  certain 
  amount 
  of 
  mobility 
  between 
  

   these 
  sterna. 
  The 
  apex 
  of 
  the 
  antennulary 
  sternum 
  fits 
  into 
  a 
  deep 
  depres- 
  

   sion 
  of 
  the 
  downward 
  process 
  of 
  the 
  rostrum, 
  but 
  can 
  easily 
  be 
  pulled 
  out 
  of 
  

   it. 
  The 
  antennary 
  sternum 
  forms 
  the 
  anterior 
  boundary 
  of 
  the 
  so-called 
  

   mouth-frame, 
  and 
  consists 
  of 
  a 
  median 
  bilobed 
  area 
  and 
  two 
  lateral 
  wing- 
  

   shaped 
  areas 
  marked 
  off 
  from 
  the 
  former 
  by 
  grooves. 
  The 
  two 
  lobes 
  of 
  the 
  

   median 
  area 
  are 
  nearly 
  square 
  in 
  outline 
  and 
  separated 
  from 
  one 
  another 
  by 
  

   a 
  deep 
  median 
  fissure 
  : 
  their 
  anterior 
  margins 
  are 
  thickened 
  and 
  truncated, 
  

   forming 
  a 
  prominent 
  ledge 
  behind 
  the 
  base 
  of 
  the 
  antennulary 
  sternum. 
  

  

  