﻿WATSON 
  : 
  NOTES 
  ON 
  HYGROMIA 
  LIMBATA 
  (dRAP.). 
  121 
  

  

  The 
  last 
  whorl 
  is 
  slightly 
  deflected 
  at 
  the 
  aperture, 
  which 
  is 
  obliquely 
  

   semi-lunar 
  and 
  a 
  little 
  broader 
  than 
  high. 
  The 
  outer 
  lip 
  is 
  expanded 
  

   excepting 
  near 
  the 
  suture, 
  and 
  has 
  an 
  internal 
  strengthening 
  rib 
  

   nearly 
  1 
  mm. 
  from 
  its 
  edge. 
  The 
  short 
  columellar 
  lip 
  is 
  almost 
  

   vertical. 
  The 
  inner 
  lip 
  is 
  extremely 
  thin, 
  and 
  so 
  is 
  the 
  periostracum 
  ; 
  

   the 
  whole 
  shell, 
  in 
  fact, 
  may 
  be 
  described 
  as 
  rather 
  thin. 
  

  

  ScDLPTUKE 
  OF 
  Shell. 
  — 
  The 
  shell 
  is 
  moderately 
  glossy, 
  but 
  the 
  

   whorls 
  are 
  crossed 
  obliquely 
  by 
  coarse 
  striae 
  corresponding 
  to 
  the 
  

   lines 
  of 
  growth, 
  and 
  many 
  specimens 
  show 
  distinct 
  traces 
  of 
  malleation 
  

   on 
  a 
  rather 
  small 
  scale. 
  When 
  viewed 
  under 
  a 
  microscope 
  extremely 
  

   tine 
  spiral 
  striae 
  are 
  also 
  seen 
  to 
  be 
  present, 
  as 
  in 
  most 
  species 
  of 
  

   Hygromia; 
  moreover, 
  all 
  the 
  whorls 
  excepting 
  the 
  first 
  two 
  are 
  

   microscopically 
  granulate. 
  The 
  granules, 
  however, 
  are 
  not 
  round, 
  

   but 
  take 
  the 
  form 
  of 
  numerous 
  little 
  ridges 
  elongated 
  in 
  a 
  direction 
  

   parallel 
  to 
  the 
  lines 
  of 
  growth 
  (pi. 
  Ill, 
  fig. 
  22). 
  These 
  minute 
  

   ridges 
  are 
  not 
  all 
  of 
  the 
  same 
  length, 
  and 
  in 
  places 
  their 
  disposition 
  

   is 
  decidedly 
  irregular; 
  but, 
  as 
  a 
  general 
  rule, 
  they 
  are 
  arranged 
  in 
  

   obli(iue 
  rows, 
  and 
  thus 
  tend 
  to 
  give 
  a 
  reticulate 
  appearance 
  to 
  the 
  

   shell 
  under 
  the 
  microscope. 
  They 
  are 
  usually 
  straight, 
  but 
  often 
  

   become 
  curved 
  in 
  the 
  peripheral 
  region 
  of 
  the 
  shell 
  near 
  the 
  aperture, 
  

   forming 
  minute 
  crescents, 
  the 
  points 
  of 
  which 
  are 
  always 
  directed 
  

   forwards. 
  The 
  thin 
  inner 
  lip, 
  together 
  with 
  the 
  outer 
  lip, 
  is 
  also 
  

   microscopically 
  granulate 
  ; 
  but 
  in 
  this 
  case 
  the 
  granules 
  are 
  round, 
  

   and 
  are 
  scattered 
  over 
  the 
  surface 
  in 
  a 
  very 
  irregular 
  manner, 
  quite 
  

   unlike 
  the 
  sculpture 
  ot 
  the 
  rest 
  of 
  the 
  shell. 
  

  

  Op.iciTY 
  AND 
  CoLouii 
  OF 
  SuELL. 
  — 
  Two 
  varieties 
  of 
  opacity 
  occur 
  in 
  

   this 
  species 
  ; 
  in 
  one 
  the 
  shell 
  is 
  entirely 
  translucent 
  except 
  for 
  the 
  

   labial 
  rib, 
  in 
  tlie 
  other 
  a 
  narrow 
  opaque 
  white 
  band 
  encircles 
  the 
  

   periphery. 
  This 
  opaque 
  band, 
  though 
  usually 
  very 
  conspicuous, 
  

   is 
  often 
  discontinuous, 
  and 
  sometimes 
  only 
  faint 
  traces 
  of 
  it 
  are 
  

   visible. 
  It 
  is 
  therefore 
  not 
  always 
  easy 
  to 
  draw 
  the 
  line 
  between 
  

   those 
  individuals 
  that 
  possess 
  the 
  band 
  and 
  those 
  that 
  do 
  not. 
  The 
  

   two 
  types 
  occur 
  both 
  in 
  England 
  and 
  in 
  France 
  ; 
  but 
  wliereas 
  the 
  

   majority 
  of 
  the 
  Englisli 
  shells 
  are 
  without 
  the 
  band, 
  in 
  France 
  tlie 
  

   larger 
  number 
  possess 
  it. 
  

  

  This 
  species 
  also 
  exhibits 
  the 
  following 
  interesting 
  series 
  of 
  colour 
  

   mutations, 
  all 
  of 
  which, 
  with 
  the 
  possible 
  exception 
  of 
  the 
  first, 
  may 
  

   be 
  combined 
  with 
  either 
  of 
  the 
  two 
  varieties 
  of 
  opacity, 
  some 
  

   specimens 
  having 
  the 
  oj)aque 
  band 
  and 
  others 
  being 
  without 
  it. 
  

  

  (.\) 
  Shell 
  entirely 
  leddish-brown 
  (excepting 
  for 
  the 
  labial 
  rib, 
  

   which 
  is 
  always 
  whiter 
  than 
  the 
  rest 
  of 
  the 
  shell). 
  This 
  seems 
  to 
  be 
  

   a 
  scarce 
  mutation 
  ; 
  the 
  writer 
  has 
  only 
  seen 
  one 
  example 
  from 
  the 
  

   Devonshire 
  locality, 
  and 
  none 
  froTu 
  abroad. 
  

  

  (B) 
  Shell 
  reddish-brown, 
  excepting 
  for 
  a 
  pale 
  uiipigmented 
  zone 
  

   round 
  the 
  periphery. 
  This 
  mutation 
  differs 
  rather 
  strikinglv 
  Irom 
  

   the 
  last, 
  since 
  the 
  pale 
  zone 
  is 
  usually 
  well 
  defined 
  — 
  more 
  so 
  than 
  in 
  

   most 
  specimens 
  of 
  the 
  variety 
  alhocinda 
  in 
  Hygromia 
  striolata 
  or 
  

   IT. 
  hispida. 
  At 
  least 
  40 
  per 
  cent, 
  of 
  the 
  English 
  examples 
  appear 
  to 
  

   belong 
  to 
  this 
  mutation, 
  and 
  it 
  probably 
  occurs 
  in 
  France 
  also, 
  

   although 
  the 
  writer 
  has 
  not 
  himself 
  found 
  it 
  on 
  the 
  Continent. 
  

  

  