﻿70 
  DR. 
  Gj 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID^ 
  : 
  

  

  antennules 
  and 
  antennae 
  are 
  extraordinarily 
  similar 
  in 
  Raninoides 
  and 
  

   Lyreidus 
  (figs. 
  36-39) 
  ; 
  so 
  also 
  are 
  details 
  in 
  the 
  first 
  and 
  second 
  and 
  even 
  in 
  

   the 
  third 
  maxillipeds. 
  In 
  all 
  these 
  things 
  the 
  relationship 
  seems 
  very 
  close, 
  

   but 
  in 
  other 
  respects 
  the 
  two 
  forms 
  are 
  divergent. 
  In 
  Li/reidus 
  the 
  eleventh 
  

   sternum 
  is 
  large 
  but 
  narrowed 
  between 
  the 
  articulations 
  of 
  the 
  first 
  pereio- 
  

   pods 
  and 
  produced 
  backwards 
  into 
  two 
  small 
  pterygoid 
  processes 
  which 
  

   form 
  the 
  sides 
  of 
  a 
  hollow 
  in 
  which 
  the 
  last 
  segment 
  of 
  the 
  abdomen 
  can 
  be 
  

   lodged, 
  as 
  described 
  above. 
  Owing 
  to 
  the 
  presence 
  of 
  these 
  pterygoid 
  

   processes 
  the 
  twelfth 
  sternum 
  appears 
  to 
  be 
  deeply 
  fitted, 
  but 
  it 
  is 
  really 
  

   short, 
  narrow, 
  and 
  flat, 
  in 
  this 
  differing 
  much 
  from 
  Raninoides. 
  The 
  thirteenth 
  

   sternum 
  being 
  also 
  short 
  the 
  coxa3 
  of 
  the 
  first 
  three 
  pairs 
  of 
  pereiopods 
  are 
  

   close 
  together, 
  and 
  in 
  this 
  respect 
  Li/reidus 
  resembles 
  Notopus 
  rather 
  than 
  

   Notopoides, 
  Notosceles, 
  or 
  Raninoides. 
  In 
  the 
  first 
  and 
  second 
  pereiopods 
  of 
  

   Lyreidus 
  the 
  iscbiomerus 
  is 
  long, 
  slender, 
  and 
  scantily 
  fringed 
  with 
  hairs 
  ; 
  

   the 
  carpus 
  rather 
  short 
  ; 
  the 
  propodus 
  nearly 
  twice 
  as 
  long 
  as 
  it 
  is 
  broad 
  ; 
  

   the 
  dactylus 
  elongate 
  and 
  almost 
  styliform, 
  with 
  a 
  strong 
  external 
  ridge. 
  In 
  

   the 
  third 
  pereiopods 
  the 
  propodus 
  is 
  about 
  as 
  broad 
  as 
  it 
  is 
  long 
  and 
  the 
  

   dactylus 
  cultriform. 
  These 
  are 
  clearly 
  digging 
  and 
  walking 
  legs, 
  and 
  one 
  

   may 
  conclude 
  that 
  the 
  descendants 
  of 
  a 
  form 
  in 
  which 
  reduction 
  of 
  the 
  

   abdomen 
  and 
  last 
  pair 
  of 
  legs 
  led 
  to 
  the 
  suppression 
  of 
  the 
  posterior 
  branchial 
  

   orifices, 
  diverged 
  as 
  they 
  adopted 
  a 
  more 
  exclusively 
  swimming 
  habit 
  into 
  

   Raninoides, 
  as 
  they 
  became 
  more 
  exclusively 
  burrowers 
  into 
  L^yreidus. 
  

   Lyreidus 
  must 
  bury 
  itself 
  deeply, 
  with 
  the 
  tip 
  of 
  its 
  narrow 
  elongated 
  snout 
  

   just 
  breaking 
  the 
  surface 
  of 
  the 
  sand. 
  Having 
  no 
  posterior 
  branchial 
  orifices 
  

   it 
  must 
  be 
  dependent 
  on 
  an 
  inhalant 
  current 
  setting 
  in 
  somewhere 
  in 
  the 
  

   region 
  of 
  the 
  snout. 
  One 
  would 
  expect 
  some 
  specialised 
  inhalant 
  apparatus, 
  

   but 
  there 
  is 
  very 
  little 
  evidence 
  of 
  such. 
  Indeed, 
  it 
  is 
  a 
  singular 
  thing 
  that 
  

   Ranina, 
  Notopus, 
  and 
  Notosceles, 
  all 
  of 
  which 
  have 
  well-developed 
  posterior 
  

   branchial 
  orifices, 
  have 
  in 
  addition 
  much 
  more 
  specialised 
  orbital 
  and 
  anten- 
  

   nary 
  arrangements 
  for 
  directing 
  the 
  flow 
  of 
  an 
  incurrent 
  respiratory 
  stream 
  

   than 
  have 
  Raninoides 
  and 
  Lyreidus, 
  in 
  which 
  posterior 
  respiratory 
  orifices 
  are 
  

   absent. 
  In 
  Notosceles 
  the 
  antennary 
  structure 
  is 
  not 
  very 
  different 
  from 
  

   that 
  of 
  Ranina. 
  The 
  flagellum 
  is 
  longer 
  (figs. 
  41 
  & 
  41a), 
  but 
  the 
  thick 
  

   shortened 
  segments 
  of 
  the 
  peduncle, 
  the 
  flabellate 
  shape 
  of 
  the 
  fourth 
  joint 
  

   with 
  its 
  fringe 
  of 
  plumose 
  hairs, 
  the 
  greatly 
  developed 
  crest 
  of 
  the 
  third 
  

   joint 
  also 
  fringed 
  with 
  hairs, 
  are 
  ver} 
  r 
  similar. 
  So 
  also 
  is 
  the 
  flabellate 
  shape 
  

   of 
  the 
  basal 
  joint 
  of 
  the 
  antennules. 
  Fig. 
  57 
  is 
  a 
  frontal 
  view 
  of 
  the 
  "face" 
  

   of 
  Notosceles 
  showing 
  the 
  antennas 
  as 
  nearly 
  as 
  I 
  can 
  draw 
  them 
  in 
  their 
  

   natural 
  position. 
  In 
  the 
  centre, 
  below 
  the 
  rostrum, 
  is 
  the 
  narrow 
  exhalant 
  

   passage 
  bounded 
  by 
  the 
  basal 
  joints 
  of 
  the 
  antennules. 
  The 
  orbits 
  are 
  closed 
  

   below 
  by 
  the 
  crests 
  of 
  third 
  segments 
  of 
  the 
  antennary 
  peduncles, 
  and 
  the 
  

   spaces 
  below 
  are 
  filled 
  in 
  by 
  the 
  proximal 
  segments 
  of 
  the 
  antennae 
  which 
  in 
  

  

  