﻿354 
  

  

  pkocep:dings 
  of 
  thk 
  malacological 
  socikty. 
  

  

  Sepjes 
  II. 
  Cadiz, 
  fkoii 
  the 
  Higher 
  Level. 
  

  

  Specimen. 
  

   G 
  

   H 
  

   I 
  

   J 
  

   K 
  

   L 
  

   Average 
  

  

  Here, 
  in 
  the 
  case 
  of 
  the 
  specimens 
  from 
  the 
  lower 
  locality, 
  an 
  

   average 
  apical 
  angle 
  of 
  120° 
  is 
  found, 
  while 
  in 
  the 
  specimens 
  from 
  the 
  

   higher 
  level 
  the 
  angle 
  is 
  far 
  more 
  acute, 
  averaging 
  90°, 
  a 
  difference 
  of 
  

   as 
  much 
  as 
  30° 
  ; 
  the 
  height 
  of 
  the 
  apex 
  averages 
  "30 
  cm. 
  in 
  the 
  former 
  

   case 
  and 
  "57 
  cm., 
  or 
  nearly 
  twice 
  the 
  height, 
  in 
  the 
  latter, 
  while 
  the 
  

   ratio 
  of 
  height 
  to 
  length 
  along 
  the 
  long 
  axis 
  is 
  in 
  the 
  one 
  case 
  "18 
  cm., 
  

   or 
  less 
  than 
  one-fifth, 
  in 
  the 
  other 
  as 
  much 
  as 
  "33, 
  or 
  nearly 
  one-third. 
  

  

  Again, 
  at 
  Tangier, 
  on 
  level 
  rocks 
  at 
  about 
  half-tide, 
  Siphonaria 
  

   exhibits 
  a 
  shell 
  which 
  is 
  comparatively 
  flat 
  and 
  an 
  apex 
  which 
  is 
  not 
  

   elevated. 
  On 
  the 
  cliffs 
  at 
  whose 
  foot 
  the 
  waves 
  break 
  at 
  high 
  tide, 
  

   and 
  where, 
  as 
  a 
  rule, 
  only 
  the 
  spray 
  can 
  reach 
  it, 
  the 
  same 
  species 
  

   shows 
  a 
  shell 
  which 
  is 
  the 
  reverse 
  ot 
  flat, 
  and 
  wliose 
  apex 
  is 
  prominent 
  

   and 
  elevated. 
  

  

  Here, 
  again, 
  although 
  the 
  Tangier 
  specimens 
  from 
  tlie 
  lower 
  level 
  

   (Figs. 
  A-F) 
  are 
  not 
  so 
  markedly 
  flat 
  as 
  those 
  from 
  Cadiz, 
  yet 
  thej' 
  

   show 
  an 
  average 
  apical 
  angle 
  of 
  105°, 
  as 
  compared 
  with 
  one 
  of 
  87'6° 
  

   from 
  shells 
  taken 
  from 
  the 
  high-tide 
  mark 
  (Figs. 
  J-jS") 
  ; 
  the 
  height 
  

   of 
  apex 
  in 
  the 
  former 
  case 
  averages 
  ■43 
  em., 
  in 
  the 
  other 
  •76, 
  or 
  not 
  

  

  