﻿46 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID.E 
  : 
  

  

  narrow 
  transverse 
  bar 
  at 
  the 
  base 
  of 
  the 
  rostrum 
  with 
  [the 
  tergum 
  of 
  the 
  

   antennulary 
  segment. 
  This 
  bar 
  is 
  easily 
  seen 
  from 
  the 
  inside, 
  but 
  does 
  not 
  

   appear 
  in 
  a 
  front 
  view, 
  being 
  concealed 
  by 
  the 
  base 
  of 
  the 
  rostrum. 
  Right 
  

   and 
  left 
  of 
  it 
  are 
  two 
  deep 
  crescentic 
  grooves 
  which 
  are 
  the 
  external 
  indica- 
  

   tion 
  of 
  two 
  deep 
  aliform 
  apodemes 
  to 
  which 
  the 
  anterior 
  gastric 
  muscles 
  are 
  

   attached. 
  The 
  apodemes 
  in 
  question 
  are 
  known 
  as 
  the 
  procephalic 
  lobes, 
  

   and 
  various 
  suggestions 
  have 
  been 
  made 
  as 
  to 
  their 
  significance, 
  but, 
  in 
  my 
  

   opinion, 
  they 
  are 
  simply 
  the 
  well-developed 
  pleural 
  apodemes 
  of 
  the 
  inter- 
  

   segment 
  i/ii. 
  Thus 
  far 
  the 
  interpretations 
  I 
  have 
  given 
  fire 
  hardly, 
  if 
  at 
  

   all, 
  at 
  variance 
  with 
  those 
  of 
  previous 
  authorities, 
  but 
  the 
  homologies 
  of 
  

   the 
  antennary 
  and 
  mandibular 
  segments 
  present 
  greater 
  difficulties. 
  The 
  

   so 
  called 
  epistome 
  of 
  ]S 
  J 
  eplirops, 
  as 
  also 
  that 
  of 
  the 
  lobster 
  and 
  the 
  crayfish, 
  

   is 
  clearly 
  made 
  up 
  of 
  two 
  parts 
  : 
  an 
  anterior 
  broad 
  plate 
  the 
  lateral 
  regions 
  

   of 
  which 
  are 
  produced 
  right 
  and 
  left 
  into 
  broad 
  divergent 
  wings, 
  giving 
  the 
  

   whole 
  the 
  shape 
  of 
  a 
  broad 
  inverted 
  V. 
  Behind 
  this, 
  fitting 
  closely 
  into 
  

   the 
  angle 
  of 
  the 
  V, 
  but 
  separated 
  from 
  it 
  by 
  a 
  distinct 
  groove, 
  is 
  a 
  somewhat 
  

   projecting 
  narrow 
  curved 
  bar 
  the 
  outer 
  extremities 
  of 
  which 
  end 
  in 
  incurved 
  

   knobs, 
  which 
  knobs 
  are 
  excavated 
  internally 
  to 
  form 
  the 
  strophidia 
  for 
  articu- 
  

   tion 
  with 
  the 
  inner 
  articular 
  processes 
  of 
  the 
  mandibles. 
  The 
  presence 
  of 
  

   these 
  strophidia 
  is 
  of 
  itself 
  evidence 
  that 
  the 
  bar 
  in 
  question 
  is 
  the 
  mandibular 
  

   sternum. 
  The 
  transverse 
  groove 
  in 
  front 
  of 
  it 
  deepens 
  in 
  the 
  middle 
  line 
  to 
  

   form 
  a 
  triangular 
  pit 
  or 
  depression 
  and 
  on 
  the 
  inner 
  surface 
  is 
  a 
  correspond- 
  

   ing 
  projection 
  — 
  in 
  fact, 
  an 
  apodeme 
  for 
  the 
  attachment 
  of 
  muscles. 
  As 
  

   transverse 
  apodemes 
  are 
  always 
  intersegmental, 
  this 
  groove 
  with 
  its 
  median 
  

   apodeme 
  indicates 
  clearly 
  enough 
  the 
  boundary 
  between 
  the 
  antennary 
  and 
  

   mandibular 
  sterna. 
  The 
  antennary 
  epimeron 
  of 
  either 
  side 
  is 
  represented 
  by 
  

   the 
  very 
  narrow 
  curved 
  bar 
  forming 
  the 
  outer 
  boundary 
  of 
  the 
  antennary 
  

   socket. 
  This 
  bar 
  is 
  united 
  by 
  a 
  membranous 
  fold 
  to 
  and 
  is 
  overlapped 
  by 
  

   the 
  fold 
  of 
  the 
  anterior 
  margin 
  of 
  the 
  carapace 
  forming 
  the 
  commencement 
  

   of 
  the 
  branchiostegite. 
  Posteriorly 
  this 
  bar 
  bends 
  inwards 
  to 
  form 
  the 
  

   thickened 
  interned 
  rim 
  of 
  the 
  antero-lateral 
  margin 
  of 
  the 
  antennary 
  

   sternum, 
  and 
  though 
  it 
  is 
  completely 
  fused 
  with 
  the 
  hitter, 
  I 
  do 
  not 
  doubt 
  

   that 
  this 
  thickened 
  rim 
  represents 
  the 
  intersegmental 
  arthrophragm 
  iii/iv. 
  

   Externally 
  the 
  antennary 
  epimeron 
  expands 
  and 
  passes, 
  without 
  any 
  obvious 
  

   line 
  of 
  demarcation, 
  into 
  the 
  calcified 
  plate 
  marked 
  a; 
  in 
  fig. 
  18. 
  In 
  

   Nephrops 
  this 
  plate 
  is 
  firmly 
  fused 
  to 
  the 
  outer 
  edge 
  of 
  the 
  V-shaped 
  

   antennary 
  sternum, 
  and 
  is 
  set 
  back 
  at 
  an 
  angle 
  to 
  it 
  in 
  such 
  wise 
  as 
  to 
  form 
  

   the 
  inner 
  and 
  upper 
  wall 
  of 
  the 
  anterior 
  part 
  of 
  the 
  exhalant 
  branchial 
  canal, 
  

   but 
  in 
  both 
  the 
  lobster 
  and 
  the 
  crayfish 
  it 
  lies 
  more 
  nearly 
  in 
  the 
  same 
  

   plane 
  as 
  the 
  antennary 
  sternum 
  and 
  takes 
  little 
  or 
  no 
  part 
  in 
  the 
  formation 
  

   of 
  the 
  branchial 
  canal. 
  The 
  postero-internal 
  margin 
  of 
  this 
  plate 
  is 
  thickened, 
  

   produced 
  backwards, 
  and 
  engages 
  in 
  a 
  groove 
  on 
  the 
  front 
  surface 
  of 
  the 
  

  

  