﻿A 
  STUDY 
  IN 
  CARCINOLOGY. 
  4 
  

  

  and 
  the 
  anlennary 
  sockets 
  lie 
  well 
  behind 
  the 
  ocular 
  peduncles 
  : 
  there 
  are 
  no 
  

  

  antennulary 
  fossae 
  internal 
  to 
  the 
  orbits. 
  The 
  ocular 
  peduncle 
  ot' 
  Ltcuiina, 
  as 
  

   is 
  well 
  known, 
  exhibits 
  these 
  calcified 
  segments 
  bent 
  at 
  an 
  angle 
  to 
  oik; 
  

   another 
  when 
  the 
  peduncle 
  is 
  retracted 
  into 
  its 
  orbit. 
  Reference 
  to 
  fig. 
  22 
  

   shows 
  that 
  there 
  are 
  similarly 
  three 
  segments 
  in 
  the 
  ocular 
  peduncle 
  of 
  

   Notopus, 
  hut 
  the 
  two 
  proximal 
  are 
  very 
  short, 
  the 
  greater 
  part 
  of 
  the 
  

   peduncle 
  being 
  formed 
  by 
  the 
  elongated 
  distal 
  segments 
  which, 
  when 
  turned 
  

   backwards 
  and 
  downwards, 
  rests 
  in 
  an 
  elongated 
  orbital 
  excavation 
  fringed 
  

   with 
  hairs. 
  There 
  is 
  no 
  division 
  of 
  the 
  orbit 
  by 
  a 
  downward 
  growth 
  of 
  the 
  

   front 
  external 
  to 
  the 
  antennules, 
  and 
  the 
  proximal 
  segments 
  of 
  the 
  ocular 
  

   peduncles 
  are 
  inserted 
  close 
  to 
  the 
  middle 
  line 
  on 
  either 
  side 
  of 
  the 
  rostral 
  

   downgrowth. 
  In 
  all 
  these 
  respects 
  the 
  Raninidse 
  have 
  departed 
  very 
  little 
  

   from 
  the 
  Astacuran 
  type 
  and 
  differ 
  from 
  the 
  more 
  cancroid 
  characters 
  

   exhibited 
  by 
  the 
  Dorippida?. 
  In 
  Notopus 
  the 
  downward 
  process 
  of 
  the 
  

   rostrum 
  is 
  narrow 
  and 
  strongly 
  keeled 
  ventrally 
  ; 
  its 
  dovetail-like 
  articu- 
  

   lation 
  with 
  the 
  antennulary 
  sternum 
  is 
  well 
  seen 
  in 
  fig. 
  22. 
  The 
  antennulary 
  

   sternum 
  is 
  escutcheon-shaped, 
  strongly 
  keeled 
  in 
  the 
  middle 
  line, 
  and 
  narrow 
  

   posteriorly. 
  It 
  has 
  a 
  certain 
  amount 
  of 
  mobility 
  on 
  the 
  antennnry 
  sternum, 
  

   which 
  latter 
  structure 
  is 
  a 
  broad 
  triangular 
  or 
  rather 
  V-shaped 
  plate 
  the 
  

   apex 
  pointing 
  forward, 
  the 
  antero-lateral 
  margins 
  raised 
  and 
  thickened 
  but 
  

   not 
  infolded 
  and 
  forming 
  part 
  of 
  the 
  inner 
  wall 
  of 
  the 
  antennary 
  sockets 
  : 
  

   more 
  posteriorly 
  these 
  margins 
  are 
  united 
  to 
  the 
  pterygostomial 
  lobes 
  of 
  the 
  

   carapace. 
  The 
  ventral 
  surface 
  of 
  the 
  antennary 
  sternum 
  is 
  deeply 
  excavated 
  

   to 
  form 
  the 
  exhalant 
  orifice 
  of 
  the 
  branchial 
  canals 
  ; 
  its 
  anterior 
  moiety 
  is 
  

   divided 
  into 
  right 
  and 
  left 
  channels 
  by 
  a 
  low 
  median 
  ridge, 
  posterior 
  to 
  which 
  

   the 
  right 
  and 
  left 
  branchial 
  canals 
  are 
  separated 
  from 
  one 
  another 
  by 
  a 
  large 
  

   ventrally 
  projecting 
  hood. 
  This 
  hood, 
  which 
  is 
  characteristic 
  of 
  the 
  Rani- 
  

   nidse, 
  is 
  the 
  greatly 
  developed 
  median 
  part 
  of 
  the 
  mandibular 
  sternum, 
  and 
  its 
  

   postero-external 
  corners 
  are 
  produced 
  right 
  and 
  left 
  into 
  curved 
  horns 
  at 
  the 
  

   extremities 
  of 
  which 
  are 
  the 
  strophidia 
  for 
  the 
  articulation 
  of 
  the 
  mandibles. 
  

   The 
  suture 
  between 
  the 
  antennary 
  and 
  mandibular 
  sternum 
  is 
  well 
  marked 
  

   in 
  all 
  the 
  Raninidse 
  I 
  have 
  examined. 
  The 
  shape 
  and 
  size 
  of 
  this 
  hood-like 
  

   mandibular 
  sternum 
  and 
  its 
  relations 
  to 
  the 
  antennary 
  sternum 
  in 
  front 
  and 
  

   the 
  labrum 
  behind 
  are 
  shown 
  for 
  Ranina 
  in 
  the 
  perspective 
  sketch 
  (fig. 
  2b'). 
  

   The 
  figure 
  also 
  shows 
  the 
  curved 
  lines 
  of 
  hairs 
  guarding 
  the 
  exit 
  of 
  the 
  

   liranchial 
  canal 
  ; 
  the 
  posterior 
  and 
  more 
  prominent 
  line 
  of 
  hairs 
  marks 
  off 
  

   an 
  oblong 
  plate 
  forming 
  part 
  of 
  the 
  roof 
  of 
  the 
  branchial 
  canal, 
  and 
  as 
  a 
  

   distinct 
  suture 
  can 
  be 
  observed 
  internally 
  corresponding 
  to 
  the 
  external 
  line 
  

   of 
  hairs, 
  I 
  identify 
  this 
  oblong 
  plate 
  with 
  the 
  mandibular 
  epimeron. 
  In 
  

   JYotopus 
  the 
  exit 
  of 
  the 
  branchial 
  canal 
  is 
  guarded 
  by 
  a 
  diffuse 
  hairy 
  

   patch, 
  and 
  the 
  area 
  behind 
  this, 
  drawn 
  out 
  into 
  the 
  triangular 
  projection 
  

   shown 
  in 
  fig. 
  22, 
  must 
  be 
  taken 
  to 
  represent 
  the 
  mandibular 
  epimeron, 
  

  

  LINN. 
  JOURN. 
  — 
  ZOOLOGY, 
  VOL. 
  XXXV. 
  4 
  

  

  