﻿48 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID^E 
  : 
  

  

  the 
  external 
  articular 
  processes 
  of 
  the 
  mandibles. 
  There 
  can 
  be 
  little 
  doubt 
  

   that 
  these 
  sire 
  the 
  epimera 
  of 
  the 
  mandibular 
  segment, 
  and 
  that 
  they 
  are 
  

   homologous 
  with] 
  the 
  less 
  sharply 
  defined 
  areas 
  similarly 
  identified 
  in 
  the 
  

   Astacura. 
  

  

  In 
  JEihusa 
  ciliatifrons 
  the 
  arrangements 
  are 
  very 
  similar 
  to 
  those 
  in 
  

   JEthusina, 
  but 
  the 
  individual 
  sclerites 
  are 
  not 
  so 
  easily 
  distinguished. 
  In 
  

   this 
  species 
  the 
  spout-shaped 
  anterior 
  end 
  of 
  the 
  antennary 
  sternum 
  is 
  pro- 
  

   duced 
  so 
  far 
  forwards 
  that 
  very 
  little 
  of 
  the 
  antennulary 
  sternum 
  can 
  be 
  

   seen 
  in 
  a 
  surface 
  view. 
  The 
  mandibles 
  also 
  are 
  reduced 
  in 
  size 
  and 
  the 
  

   mandibular 
  sternum 
  is 
  membranous. 
  In 
  Dorippe 
  lanata 
  the 
  spout-like 
  

   anterior 
  end 
  of 
  the 
  antennary 
  sternum 
  is 
  produced 
  forward 
  to 
  such 
  an 
  extent 
  

   that 
  it 
  articulates 
  with 
  and 
  overlaps 
  the 
  downward 
  process 
  of 
  the 
  rostrum, 
  

   thus 
  completely 
  concealing 
  the 
  antennulary 
  sternum. 
  This 
  is 
  one 
  of 
  the 
  

   rare 
  instances 
  in 
  which 
  union 
  is 
  effected 
  between 
  the 
  rostral 
  process 
  and 
  

   the 
  antennary 
  sternum. 
  In 
  Dorippe 
  as 
  in 
  JEtliusa 
  the 
  mandibular 
  sternum 
  

   is 
  almost 
  wholly 
  membranous, 
  exhibiting 
  only 
  two 
  small 
  calcifications 
  in 
  the 
  

   region 
  of 
  the 
  strophidia. 
  The 
  mandibular 
  epimera 
  rre 
  large 
  and 
  distinct, 
  

   triangular 
  in 
  shape, 
  the 
  apices 
  of 
  the 
  triangle 
  produced 
  backwards. 
  The 
  

   body 
  of 
  the 
  antennary 
  sternum 
  exhibits 
  a 
  large 
  central 
  boss 
  in 
  front 
  of 
  the 
  

   mandibular 
  sternum, 
  which 
  might, 
  at 
  first 
  sight, 
  be 
  taken 
  for 
  a 
  forward 
  

   median 
  extension 
  of 
  the 
  latter, 
  but 
  it 
  obviously 
  has 
  no 
  connection 
  with 
  it. 
  

  

  After 
  this 
  survey 
  of 
  one 
  of 
  the 
  families 
  of 
  the 
  Oxystomatous 
  crabs, 
  the 
  

   Raninidse 
  may 
  be 
  brought 
  into 
  comparison. 
  Fig. 
  22 
  is 
  a 
  front 
  view 
  of 
  

   the 
  present 
  region 
  of 
  Notopus 
  dorsipes, 
  all 
  the 
  appendages 
  being 
  removed 
  

   with 
  the 
  exception 
  of 
  the 
  right 
  mandible 
  and 
  the 
  left 
  ocular 
  peduncle. 
  

   Fig. 
  23 
  is 
  a 
  similar 
  view 
  of 
  Ranina 
  dentata, 
  and 
  figs. 
  24 
  and 
  25 
  illustrate 
  the 
  

   same 
  regions 
  in 
  Notosceles 
  and 
  Lyreidus. 
  For 
  descriptive 
  purposes 
  Notopus, 
  

   a 
  less 
  modified 
  genus 
  than 
  Ranina 
  or 
  Lyreidus, 
  will 
  be 
  taken 
  as 
  the 
  example 
  

   of 
  the 
  family. 
  The 
  first 
  thing 
  to 
  be 
  observed 
  is 
  that 
  the 
  antennary 
  sockets 
  

   are 
  relatively 
  large 
  and 
  situated 
  behind 
  rather 
  than 
  to 
  the 
  sides 
  of 
  the 
  

   antennulary 
  sockets. 
  In 
  this 
  respect 
  Notopus 
  more 
  nearly 
  resembles 
  

   Homarus 
  than 
  Nephrops, 
  for 
  in 
  the 
  latter 
  the 
  antennary 
  sockets 
  are 
  dis- 
  

   placed 
  laterally. 
  Reference 
  to 
  fig. 
  29 
  shows 
  that 
  in 
  Notopus, 
  as 
  in 
  all 
  

   Raninidse, 
  the 
  antennary 
  peduncle 
  is 
  five-jointed, 
  the 
  basal 
  joint 
  being 
  freely 
  

   moveable, 
  short 
  antero-posteriorly 
  but 
  of 
  relatively 
  considerable 
  width 
  ven- 
  

   trally, 
  and 
  it 
  bears 
  the 
  excretory 
  aperture 
  on 
  a 
  distinct 
  prominent 
  tubercle. 
  

  

  In 
  Notopus 
  and 
  in 
  Ranilia, 
  M. 
  Edw., 
  the 
  antennary 
  flagellum 
  is 
  multi- 
  

   articulate 
  and 
  of 
  considerable 
  length, 
  with 
  special 
  features 
  which 
  will 
  be 
  

   referred 
  to 
  later. 
  All 
  these 
  characters 
  are 
  Macruran. 
  The 
  antennules 
  

   (fb>-. 
  28) 
  with 
  their 
  enlarged 
  basal 
  segments 
  and 
  abbreviated 
  few-jointed 
  

   external 
  and 
  internal 
  flagella 
  are 
  more 
  cancroid 
  in 
  character, 
  but 
  the 
  basal 
  

   joints 
  are 
  not 
  inflated 
  to 
  anything 
  like 
  the 
  same 
  extent 
  as 
  in 
  the 
  Dorippidse 
  

  

  