﻿66 
  DR. 
  G. 
  O. 
  BOURNE 
  ON 
  THE 
  RANINID^E 
  : 
  

  

  Among 
  other 
  genera, 
  Zanclifer 
  and 
  Notopoides, 
  though 
  their 
  antennary 
  

   flagella 
  are 
  not 
  so 
  much 
  reduced, 
  are 
  in 
  all 
  essential 
  respects 
  so 
  similar 
  to 
  

   Ranina 
  that 
  it 
  can 
  hardly 
  be 
  doubted 
  that 
  they 
  have 
  similar 
  habits 
  and 
  are 
  

   equally 
  adaptable 
  as 
  regards 
  their 
  respiratory 
  processes. 
  Zanclifer 
  differs 
  

   from 
  all 
  other 
  Raninidse 
  in 
  having 
  normal, 
  i.e. 
  not 
  feathered 
  and 
  differenti- 
  

   ated, 
  chelipeds, 
  and 
  it 
  may 
  be 
  that 
  it 
  is 
  more 
  nearly 
  related 
  to 
  the 
  ancestral 
  

   form 
  than 
  Notopus. 
  It 
  has 
  all 
  the 
  external 
  characteristics 
  of 
  a 
  burrowing 
  

   crab. 
  Notopoides, 
  on 
  the 
  other 
  hand, 
  is 
  much 
  more 
  closely 
  related 
  to 
  

   Notopus, 
  from 
  which 
  it 
  differs 
  mainly 
  in 
  the 
  elongation 
  of 
  the 
  twelfth 
  

   sternum, 
  whereby 
  the 
  second, 
  third, 
  aid 
  fourth 
  pereiopods 
  are 
  shifted 
  back- 
  

   wards 
  and 
  form 
  a 
  posterior 
  group 
  of 
  legs, 
  separated 
  by 
  a 
  space 
  from 
  the 
  first 
  

   pereiopods 
  : 
  this 
  feature 
  is 
  exhibited 
  to 
  a 
  more 
  marked 
  degree 
  in 
  Notosceles 
  

   (fig. 
  3) 
  and 
  is 
  carried 
  to 
  an 
  extreme 
  in 
  Raninoides 
  (fig. 
  6). 
  In 
  each 
  genus 
  

   the 
  increase 
  in 
  length 
  of 
  the 
  twelfth 
  sternum 
  is 
  correlated 
  with 
  a 
  reduction 
  

   in 
  size 
  of 
  the 
  last 
  pair 
  of 
  pereiopods, 
  a 
  progressive 
  narrowing 
  of 
  the 
  abdomen, 
  

   a 
  reduction 
  in 
  the 
  size 
  and 
  functional 
  importance 
  of 
  the 
  posterior 
  branchial 
  

   orifices, 
  and 
  progressive 
  modifications 
  of 
  the 
  second 
  and 
  third 
  pereiopods 
  

   indicative 
  of 
  their 
  increasing 
  use 
  as 
  swimming 
  organs. 
  A 
  comparison 
  of 
  the 
  

   series 
  Rani?ia, 
  Notopus, 
  Notopoides, 
  Notosceles, 
  Raninoides, 
  leads 
  me 
  to 
  the 
  

   conclusion 
  that, 
  whilst 
  all 
  of 
  them 
  are 
  to 
  a 
  greater 
  or 
  less 
  extent 
  sand- 
  

   burrowers, 
  the 
  first-named 
  during 
  its 
  periods 
  of 
  activity 
  progresses 
  mainly 
  

   by 
  crawling 
  and 
  is 
  a 
  poor 
  swimmer. 
  Notopus 
  and 
  Notopoides 
  crawl 
  and 
  

   swim 
  ; 
  Notosceles 
  is 
  a 
  fairly 
  efficient 
  and 
  Raninoides 
  a 
  very 
  efficient 
  

   swimmer. 
  This 
  conclusion 
  I 
  will 
  now 
  endeavour 
  to 
  justify. 
  

  

  Notopoides 
  is 
  obviously 
  a 
  burrowing 
  crab 
  ; 
  the 
  sandy 
  condition 
  of 
  the 
  

   specimens 
  in 
  the 
  Natural 
  History 
  Museum 
  bears 
  testimony 
  to 
  this 
  habit. 
  

   In 
  most 
  of 
  the 
  structural 
  features 
  subservient 
  to 
  the 
  respiratory 
  processes 
  

   Notopoides 
  bears 
  a 
  strong 
  resemblance 
  to 
  Notopus. 
  Attention 
  may 
  be 
  

   directed 
  specially 
  to 
  the 
  following 
  points 
  : 
  the 
  last 
  pair 
  of 
  pereiopods 
  are 
  not 
  

   much 
  reduced 
  in 
  size 
  and 
  all 
  their 
  joints 
  are 
  densely 
  fringed 
  with 
  hairs 
  ; 
  the 
  

   tergum 
  of 
  the 
  first 
  abdominal 
  somite 
  is 
  as 
  broad 
  as 
  the 
  posterior 
  margin 
  of 
  

   the 
  carapace 
  ; 
  the 
  posterior 
  branchial 
  orifices 
  are 
  patent 
  and 
  give 
  evidence 
  

   of 
  their 
  function 
  as 
  inhalant 
  passages 
  ; 
  the 
  exposed 
  portions 
  of 
  the 
  epimera 
  

   of 
  the 
  eleventh, 
  twelfth, 
  and 
  thirteenth 
  somites'are 
  concave 
  and 
  overhung 
  by 
  

   the 
  edge 
  of 
  the 
  branchiostegite 
  ; 
  the 
  chelipeds 
  are 
  adapted 
  for 
  raking 
  sand 
  

   from 
  under 
  the 
  thorax. 
  In 
  short, 
  all 
  the 
  adaptations 
  described 
  in 
  Notojms 
  

   and 
  Ranina 
  for 
  maintaining 
  a 
  respiratory 
  current 
  through 
  the 
  posterior 
  

   respiratory 
  orifices 
  are 
  present 
  to 
  an 
  equal 
  degree 
  in 
  Notopoides. 
  This 
  

   genus 
  must 
  be 
  equally 
  addicted 
  to 
  the 
  burrowing 
  habit, 
  but 
  the 
  articulations 
  

   and 
  characters 
  of 
  its 
  last 
  three 
  pairs 
  of 
  pereiopods 
  suggest 
  that, 
  when 
  active, 
  

   it 
  is 
  to 
  some 
  considerable 
  extent 
  a 
  swimmer. 
  

  

  In 
  Notosceles 
  the 
  adaptations 
  for 
  maintaining 
  a 
  posterior 
  inhalant 
  

   respiratory 
  current 
  are 
  still 
  recognizable, 
  but 
  are 
  obviously 
  less 
  efficient. 
  

  

  