﻿ASTACUS 
  PLUVIATIL18. 
  361 
  

  

  He 
  recognised 
  two 
  kinds, 
  tlie 
  stone-crayfish 
  and 
  the 
  noble- 
  

   crayfish, 
  which 
  he 
  called 
  Astacus 
  torrentiuni 
  (Schrank), 
  

   and 
  Astacus 
  nobilis 
  (Huxley). 
  He 
  mentions 
  that 
  A. 
  

   torrentiuni 
  never 
  has 
  more 
  than 
  two 
  rudimentary 
  pleuro- 
  

   branchs, 
  whereas 
  he 
  had 
  found 
  three 
  in 
  A 
  . 
  n 
  o 
  b 
  i 
  1 
  i 
  s 
  . 
  The 
  stone- 
  

   crayfish 
  A. 
  torrentium 
  was 
  the 
  same 
  as 
  that 
  found 
  in 
  

   England, 
  and 
  he 
  left 
  it 
  an 
  open 
  question 
  whether 
  they 
  were 
  

   both 
  varieties 
  of 
  A. 
  fluviatilis, 
  or 
  whether 
  they 
  were 
  

   specifically 
  difPerent, 
  in 
  which 
  case 
  A. 
  nobilis 
  was 
  the 
  true 
  

   A. 
  fluviatilis. 
  

  

  Of 
  A. 
  leptodactylus, 
  and 
  the 
  closely 
  allied 
  forms 
  A. 
  

   pachypus 
  and 
  A. 
  angulosus, 
  Professor 
  Huxley 
  says 
  that 
  

   "if 
  A. 
  angulosus 
  and 
  A. 
  pachypus 
  are 
  varieties 
  of 
  

   A. 
  leptodactylus, 
  I 
  cannot 
  see 
  why 
  Gerstfeldt's 
  conclusion 
  

   that 
  A. 
  nobilis 
  is 
  another 
  variety 
  of 
  the 
  same 
  form 
  need 
  be 
  

   questioned 
  on 
  morphological 
  grounds." 
  Faxon^ 
  and 
  Ortmann^ 
  

   recognise 
  the 
  following 
  European 
  species: 
  Astacus 
  fluvia- 
  

   tilis,Fabr.,'A.leptodactylus 
  Esch.,A.p 
  alii 
  pes 
  Lereb.,^ 
  A. 
  

   torrentium 
  Schrk., 
  A. 
  pachypus 
  Rthke. 
  and 
  A. 
  colchicus 
  

   Kessl., 
  which 
  differ 
  from 
  each 
  other 
  not 
  only 
  in 
  colour 
  and 
  in 
  

   the 
  form 
  of 
  the 
  rostrum 
  and 
  limbs, 
  but 
  also 
  in 
  some 
  cases 
  in 
  

   the 
  number 
  of 
  rudimentary 
  pleurobranchiae 
  in 
  the 
  "hinder 
  

   somites 
  of 
  the 
  gill-bearing 
  region. 
  

  

  Whilst 
  A. 
  fluviatilis, 
  A. 
  leptodactylus, 
  A, 
  pachypus, 
  

   and 
  A. 
  colchicus 
  have 
  three 
  rudimentary 
  pleurobranchiae, 
  

   A. 
  pallipes 
  has 
  only 
  two, 
  the 
  third 
  most 
  anterior 
  rudiment 
  

   having 
  been 
  reduced 
  to 
  a 
  minute 
  papilla, 
  and 
  A. 
  torrentium 
  

   has 
  two 
  without 
  the 
  least 
  trace 
  of 
  the 
  third. 
  

  

  The 
  crayfishes 
  which 
  are 
  used 
  by 
  students 
  in 
  University 
  

   and 
  college 
  classes 
  in 
  this 
  country 
  are 
  supplied 
  by 
  London 
  

   agents, 
  as 
  a 
  rule, 
  who 
  make 
  a 
  regular 
  business 
  of 
  importing 
  

  

  » 
  'Mem. 
  Mus. 
  Conip. 
  Zool.,' 
  Harvard, 
  x 
  (i), 
  1SS5, 
  and 
  ' 
  Proc. 
  U. 
  S. 
  Nat. 
  

   Mus.,' 
  XX, 
  pp. 
  643-694, 
  1898. 
  

  

  2 
  ' 
  Proc. 
  Anier. 
  Phil. 
  Soc.,' 
  xli, 
  p. 
  286, 
  1902. 
  

  

  ' 
  The 
  A. 
  astacus 
  (Linn.) 
  of 
  Faxon's 
  later 
  paper. 
  Ortmann 
  employs 
  tlie 
  

   generic 
  name 
  Potamobius 
  iu 
  place 
  of 
  Astacus. 
  

  

  * 
  Huxley's 
  A. 
  torrentium 
  included 
  this 
  and 
  the 
  following 
  species. 
  

  

  