﻿A 
  STUDY 
  IN 
  CARCINOLOGV. 
  67 
  

  

  I 
  In 
  1 
  last 
  pair 
  of 
  pereiopods, 
  though 
  much 
  reduced 
  in 
  size, 
  is 
  sufficiently 
  

   liberally 
  provided 
  with 
  hairy 
  fringes 
  to 
  form 
  an 
  effective 
  covering 
  for 
  the 
  

  

  roof 
  of 
  the 
  water-chambers 
  enclosed 
  between 
  the 
  other 
  pereiopods 
  and 
  the 
  

   thoracic 
  flanks. 
  The 
  epimera 
  forming 
  these 
  flanks, 
  however, 
  are 
  not 
  so 
  

   deeply 
  concave 
  as 
  in 
  Notopoides, 
  and 
  the 
  posterior 
  branchial 
  orifices, 
  though 
  

   distinct 
  enough, 
  are 
  smaller 
  and 
  obviously 
  of 
  less 
  functional 
  importance. 
  

   The 
  dactylus 
  of 
  the 
  last 
  pair 
  of 
  pereiopods 
  is 
  small, 
  elliptical, 
  and 
  clearly 
  

   better 
  adapted 
  for 
  natation 
  than 
  for 
  digging. 
  

  

  Before 
  entering 
  into 
  a 
  discussion 
  of 
  the 
  transition 
  from 
  digging 
  to 
  

   swimming 
  limbs 
  it 
  should 
  be 
  premised 
  that 
  in 
  the 
  pereiopods 
  of 
  all 
  the 
  

   llaninidse 
  the 
  articulation 
  of 
  the 
  dactylus 
  to 
  the 
  propodus 
  is 
  singularly 
  like 
  

   that 
  of 
  the 
  tarsi 
  of 
  the 
  whirligig-beetle 
  Qyrinus, 
  familiar 
  to 
  all 
  naturalists 
  

   from 
  the 
  illuminating 
  description 
  of 
  Miall. 
  Generally, 
  in 
  the 
  Raninidse, 
  the 
  

   carpus 
  is 
  moderately 
  long, 
  triangular 
  in 
  shape, 
  with 
  an 
  extensive 
  basal 
  

   articulation 
  for 
  the 
  propodus. 
  The 
  propodus 
  is 
  a 
  short 
  and 
  broad 
  oblong, 
  

   more 
  or 
  less 
  flattened, 
  with 
  a 
  very 
  small 
  articulation 
  for 
  the 
  dactylus 
  close 
  

   behind 
  its 
  postero-external 
  angle. 
  The 
  dactylus 
  is 
  very 
  variable 
  in 
  shape. 
  

   Generally 
  in 
  the 
  first 
  two 
  pereiopods 
  it 
  is 
  lanceolate 
  and 
  obviously 
  efficient 
  

   in 
  digging, 
  but 
  in 
  the 
  last 
  two 
  pereiopods 
  something 
  between 
  crescentic 
  and 
  

   cleaver-shaped 
  like 
  an 
  oriental 
  u 
  kukri." 
  In 
  either 
  case 
  it 
  is 
  so 
  articulated 
  

   by 
  a 
  narrow 
  pedicle 
  to 
  one 
  end 
  of 
  the 
  oblong 
  propodus 
  that 
  it 
  can 
  be 
  slid 
  

   behind 
  the 
  latter 
  as 
  the 
  sticks 
  of 
  a 
  lady's 
  fan 
  slide 
  over 
  one 
  another. 
  A 
  

   very 
  similar 
  form 
  of 
  limb 
  with 
  yet 
  more 
  elaborate 
  adaptive 
  details 
  is 
  seen 
  in 
  

   Matuta 
  which, 
  like 
  the 
  Raninidse, 
  is 
  at 
  once 
  a 
  swimming 
  and 
  a 
  burrowing 
  

   crab. 
  It 
  is 
  presumed 
  that 
  the 
  lanceolate 
  form 
  of 
  dactylus 
  is 
  more 
  useful 
  as 
  

   a 
  pick, 
  the 
  kukri-shaped 
  dactylus 
  as 
  a 
  shovel, 
  but 
  the 
  latter 
  may 
  be 
  service- 
  

   able 
  in 
  swimming, 
  just 
  as 
  a 
  shovel 
  may 
  on 
  emergency 
  be 
  used 
  as 
  a 
  paddle. 
  

   In 
  Zanclifer 
  the 
  dactyli 
  of 
  all 
  the 
  pereiopods 
  are 
  narrow 
  and 
  sickle-shaped 
  ; 
  

   they 
  seem 
  ill 
  adapted 
  for 
  swimming 
  but 
  effective 
  instruments 
  for 
  digging. 
  

   The 
  criterion 
  for 
  deciding 
  whether 
  a 
  limb 
  is 
  utilised 
  for 
  swimming 
  or 
  for 
  

   digging 
  consists 
  in 
  the 
  length 
  and 
  mobility 
  of 
  its 
  joints. 
  The 
  short 
  strong 
  

   limbs 
  olRanina 
  showing 
  restricted 
  mobility 
  at 
  the 
  joints 
  are 
  clearly 
  fossorial 
  

   and 
  ill 
  adapted 
  for 
  natation 
  : 
  the 
  somewhat 
  longer 
  and 
  more 
  mobile 
  limbs 
  of 
  

   Notopus 
  and 
  Notopoides 
  are, 
  however, 
  serviceable 
  for 
  both 
  purposes. 
  In 
  

   Notoscele 
  s 
  (figs. 
  2 
  & 
  3) 
  the 
  dactylus 
  of 
  the 
  second 
  pereiopods 
  is 
  sickle-shaped 
  

   as 
  in 
  Zanclifer, 
  and 
  it 
  may 
  be 
  inferred 
  that 
  this 
  pair 
  of 
  limbs 
  is 
  specialised 
  

   for 
  digging, 
  but 
  it 
  can 
  hardly 
  be 
  doubted 
  that 
  the 
  broad 
  kukri-shaped 
  

   dactylus 
  of 
  the 
  third 
  pair, 
  hinged 
  fanwise 
  to 
  the 
  outer 
  angle 
  of 
  the 
  trans- 
  

   versely 
  elongated 
  propodus 
  and 
  provided 
  with 
  a 
  marginal 
  fringe 
  of 
  long 
  setae, 
  

   is 
  specially 
  adapted 
  for 
  swimming. 
  The 
  reduced 
  fourth 
  pereiopods 
  of 
  this 
  

   genus, 
  with 
  their 
  small 
  flat 
  elliptical 
  dactyli, 
  can 
  hardly 
  be 
  of 
  any 
  value 
  in 
  

   digging 
  and 
  are 
  rather 
  suggestive 
  of 
  steering 
  paddles. 
  

  

  5* 
  

  

  