﻿ASTACUS 
  FLTJVIATILIS. 
  365 
  

  

  In 
  a 
  specimen 
  of 
  Nephrops 
  norvegicus, 
  lent 
  me 
  by 
  

   the 
  British 
  Museum, 
  in 
  exactly 
  the 
  same 
  position 
  as 
  the 
  

   cushion 
  in 
  A. 
  flu 
  via 
  til 
  is 
  is 
  a 
  partly 
  calcified 
  flap 
  which 
  

   hooks 
  over 
  the 
  epipodite 
  of 
  the 
  same 
  somitOj 
  and 
  apparently 
  

   serves 
  to 
  prevent 
  its 
  coming 
  forward. 
  In 
  Homarus 
  vul- 
  

   garis 
  this 
  hook 
  is 
  larger 
  and 
  easier 
  to 
  make 
  out. 
  

  

  A 
  specimen 
  of 
  Cam 
  bar 
  us 
  (rustic 
  us?) 
  male, 
  from 
  British 
  

   North 
  America, 
  had 
  in 
  the 
  same 
  position 
  a 
  small 
  hard 
  knob 
  ; 
  

   one 
  of 
  A. 
  torrentium 
  (male) 
  , 
  from 
  Bavaria, 
  had 
  a 
  small 
  hard 
  

   cushion 
  in 
  the 
  same 
  position. 
  Another 
  of 
  A. 
  leptodactylus 
  

   female, 
  Asia 
  Minor, 
  also 
  had 
  a 
  cushion 
  in 
  the 
  same 
  position. 
  

  

  According 
  to 
  W. 
  Faxon 
  'Hhe 
  gills 
  of 
  A. 
  gambelii 
  present 
  

   the 
  nearest 
  appi'oach 
  to 
  the 
  primitive 
  type 
  of 
  any 
  living 
  

   members 
  o£ 
  the 
  genus 
  Astacus," 
  in 
  that 
  the 
  three 
  rudi- 
  

   mentary 
  pleurobranchife 
  are 
  jointed 
  near 
  their 
  base 
  and 
  

   possess, 
  the 
  middle 
  pair 
  two 
  short 
  lateral 
  brandies, 
  and 
  the 
  

   anterior 
  and 
  posterior 
  pairs 
  one 
  short 
  lateral 
  branch, 
  at 
  

   the 
  joints. 
  Unless 
  this 
  species 
  proves 
  also 
  to 
  possess 
  

   the 
  new 
  rudimentary 
  arthrobranch, 
  its 
  gill 
  formula 
  must, 
  

   however, 
  be 
  considered 
  less 
  primitive 
  than 
  that 
  of 
  A. 
  

   fluviatilis. 
  

  

  In 
  conclusion, 
  I 
  take 
  the 
  opportunity 
  of 
  thanking 
  Professor 
  

   Ray 
  Lankester 
  for 
  kindly 
  helping 
  me 
  to 
  write 
  this 
  paper, 
  

   and 
  for 
  enabling 
  me 
  to 
  examine 
  the 
  specimens 
  in 
  the 
  British 
  

   Museum, 
  and 
  Dr. 
  Caiman 
  for 
  helping 
  me 
  in 
  so 
  doing, 
  and 
  for 
  

   important 
  assistance 
  as 
  to 
  the 
  crustacean 
  gill 
  generally. 
  

  

  Oxford, 
  October, 
  1904. 
  

  

  EXPLANATION 
  OF 
  PLATES 
  23 
  & 
  24, 
  

  

  Illustrating 
  Margery 
  Moseley's 
  paper, 
  " 
  On 
  the 
  Existence 
  of 
  

   an 
  Anterior 
  Rudimentary 
  Gill 
  in 
  Astacus 
  Fluviatilis." 
  

  

  PLA.TE 
  23. 
  

   Fig. 
  1. 
  — 
  Left 
  anterior 
  rudimentary 
  gill 
  in 
  situ 
  from 
  a 
  male, 
  31 
  inches 
  

   in 
  length 
  (from 
  tip 
  of 
  rostrum 
  to 
  end 
  of 
  telson). 
  Magnified 
  35 
  diameters. 
  

  

  