﻿136 
  

  

  PROCKEDINGS 
  OF 
  THI5 
  MALACOI-OGICAt, 
  SOCIETY. 
  

  

  a 
  depressa 
  radula 
  is 
  37 
  '4 
  mm. 
  The 
  

   in 
  lengtli 
  in 
  favour 
  of 
  vulgata 
  is, 
  in 
  

   series, 
  75"96 
  cm., 
  or 
  about 
  2^ 
  feet. 
  

  

  sum 
  of 
  the 
  wliole 
  of 
  the 
  differences 
  

   the 
  twenty-nine 
  specimens 
  of 
  the 
  

  

  It 
  must 
  be 
  remembered 
  tliat 
  the 
  specimens 
  examined 
  are 
  not 
  

   specially 
  selected 
  in 
  order 
  to 
  exhibit 
  differences 
  of 
  length 
  in 
  the 
  

   radula. 
  They 
  are 
  simply, 
  in 
  each 
  case, 
  the 
  first 
  two 
  specimens 
  of 
  

   equal 
  length 
  which 
  happened 
  to 
  come 
  to 
  hand 
  on 
  a 
  certain 
  beach 
  in 
  

   iSouth 
  Devon. 
  

  

  In 
  the 
  teeth 
  of 
  the 
  radulfe 
  themselves 
  certain 
  small 
  differences 
  appear. 
  

   In 
  both 
  cases 
  there 
  are 
  four 
  uncini 
  flanked 
  on 
  each 
  side 
  by 
  laterals, 
  the 
  

   innermost 
  of 
  which 
  is 
  armed, 
  and 
  not 
  in 
  the 
  same 
  plane 
  with 
  the 
  rest. 
  

   In 
  depressa 
  the 
  two 
  interior 
  uncini 
  are 
  much 
  narrower 
  than 
  the 
  two 
  

   externa], 
  the 
  hooks 
  being 
  mounted 
  on 
  narrower 
  bases 
  than 
  in 
  vulffata. 
  

   This 
  fact, 
  which 
  is 
  observable 
  in 
  the 
  nascent 
  rows, 
  becomes 
  more 
  

   marked 
  as 
  growth 
  proceeds. 
  In 
  vtdgata, 
  on 
  the 
  other 
  hand, 
  the 
  two 
  

   interior 
  uncini, 
  although 
  smaller 
  than 
  the 
  other 
  two, 
  are 
  not 
  nearly 
  

   so 
  unequal 
  to 
  them 
  in 
  breadth. 
  Further, 
  the 
  serrations 
  of 
  the 
  interior 
  

   lateral 
  appear 
  to 
  be 
  much 
  more 
  deeply 
  cut 
  in 
  vulgata 
  than 
  in 
  depresna. 
  

  

  The 
  sum 
  of 
  all 
  these 
  observations 
  seems 
  to 
  tend 
  decisively 
  to 
  the 
  

   conclusion 
  that 
  in 
  vulgata 
  and 
  depressa 
  we 
  have 
  two 
  quite 
  distinct 
  

   species 
  of 
  British 
  limpets. 
  It 
  is 
  my 
  impression, 
  which 
  I 
  have 
  not 
  yet 
  

   had 
  time 
  to 
  verify, 
  that 
  vulgata 
  is 
  a 
  northern, 
  depressa 
  a 
  southern 
  

  

  ^ 
  Measurements 
  are 
  in 
  millimetres. 
  

  

  