﻿116 
  PROCEEDINGS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  straight, 
  median 
  valves 
  beaked. 
  Colour 
  generally 
  gi'een, 
  end-valves 
  

   and 
  lateral 
  areas 
  of 
  median 
  valves 
  concentrically 
  lined 
  with 
  white 
  or 
  

   pale 
  greenish, 
  dorsal 
  area 
  with 
  dark-brown 
  triangular 
  patch, 
  apex 
  of 
  

   triangle 
  posterior, 
  sides 
  orange 
  marbled; 
  pleura 
  green, 
  with 
  furrows 
  

   in 
  some 
  cases 
  blue-lined. 
  In 
  some 
  specimens 
  the 
  orange 
  marbling 
  

   overruns 
  the 
  dark 
  dorsal 
  patcli, 
  and 
  also 
  extends 
  on 
  the 
  pleura, 
  the 
  

   ribs 
  becoming 
  orange-brown. 
  The 
  general 
  appearance 
  is, 
  however, 
  

   more 
  or 
  less 
  uniform. 
  On 
  the 
  tail-valve 
  there 
  is 
  a 
  very 
  narrow 
  white 
  

   patch, 
  more 
  or 
  less 
  ti'iangular 
  from 
  the 
  mucro 
  to 
  the 
  girdle, 
  where 
  

   a 
  broader 
  and 
  more 
  extensive 
  white 
  patch 
  is 
  observed. 
  Anterior 
  valve 
  

   very 
  perpendicular, 
  smooth. 
  In 
  senile 
  shells 
  an 
  obsolete 
  radial 
  ribbing 
  

   may 
  be 
  distinguished 
  under 
  a 
  strong 
  lens. 
  Median 
  valves 
  have 
  the 
  

   lateral 
  areas 
  well 
  raised 
  and 
  smooth, 
  but 
  in 
  senile 
  shells 
  concentric 
  

   growth-lines 
  are 
  prominent 
  and 
  obsolete 
  radial 
  ribbing 
  is 
  rarely 
  

   present. 
  The 
  pleural 
  areas 
  are 
  cut 
  by 
  longitudinal 
  furrows 
  which 
  are 
  

   distant 
  and 
  reach 
  across 
  the 
  valve 
  for 
  half 
  its 
  height, 
  fading 
  away 
  as 
  

   the 
  jugum 
  is 
  approached. 
  In 
  other 
  words 
  tlie 
  pleura 
  are 
  sculptured 
  

   with 
  shallow 
  ribs, 
  a 
  broad 
  smooth 
  triangle 
  being 
  observed 
  on 
  the 
  

   jugum. 
  In 
  the 
  type 
  figured 
  ten 
  grooves 
  can 
  be 
  counted 
  on 
  the 
  half- 
  

   valve, 
  four 
  of 
  which 
  extend 
  across 
  tlie 
  valve 
  ; 
  in 
  the 
  largest 
  specimen 
  

   sixteen 
  grooves 
  appear, 
  seven 
  extending 
  across 
  the 
  valve. 
  Tail-valve 
  

   with 
  the 
  mucro 
  elevated 
  at 
  the 
  posterior 
  third, 
  the 
  posterior 
  slope 
  

   slightly 
  concave 
  and 
  smooth, 
  the 
  anterior 
  area 
  sculptured 
  like 
  pleural 
  

   areas. 
  Girdle-scales 
  shining, 
  obsoletely 
  striate, 
  and 
  of 
  varied 
  colours. 
  

   Hounded 
  in 
  shape, 
  they 
  are 
  much 
  smaller 
  near 
  the 
  girdle-margin, 
  and 
  

   are 
  largest 
  in 
  the 
  centre 
  of 
  the 
  girdle. 
  Internal 
  features 
  typical 
  of 
  

   Rhyssoplax. 
  Sinus 
  very 
  narrow. 
  Colour 
  inside 
  pale 
  blue-green 
  with 
  

   the 
  sutural 
  laminae 
  white. 
  

  

  Type 
  from 
  Norfolk 
  Bay, 
  southern 
  Tasmania. 
  

  

  Length 
  31, 
  breadth 
  17 
  mm. 
  

  

  Range: 
  soutliern 
  Tasmania. 
  

  

  This 
  shell 
  has 
  been 
  known 
  as 
  Chiton 
  jtigosus, 
  but 
  it 
  differs 
  at 
  sight 
  

   from 
  the 
  typical 
  Sydney 
  shell 
  in 
  the 
  pleural 
  sculpture. 
  It 
  seems 
  

   more 
  nearly 
  allied 
  to 
  C. 
  torri 
  = 
  torriamis, 
  Hedley 
  & 
  Hull, 
  but 
  it 
  

   cannot 
  be 
  regarded 
  as 
  a 
  subspecies 
  thereof, 
  nor 
  can 
  it 
  be 
  so 
  classed 
  in 
  

   connexion 
  with 
  R. 
  jtigosa. 
  We 
  give 
  diagrams 
  of 
  sections 
  through 
  

   the 
  pleural 
  areas 
  of 
  each 
  species, 
  taken 
  at 
  right 
  angles 
  to 
  the 
  girdle 
  

   (PI. 
  V. 
  Fig. 
  \a 
  and 
  a"). 
  In 
  South 
  Australia 
  there 
  lives 
  another 
  species, 
  

   classed 
  as 
  C.j'ugosus, 
  which 
  is 
  nearer 
  to 
  that 
  form, 
  but 
  it 
  lives 
  with 
  

   Ji. 
  torriana, 
  and 
  so 
  complicates 
  the 
  matter. 
  Moreover, 
  the 
  West 
  

   Australian 
  shell 
  called 
  li. 
  torriana 
  differs 
  at 
  sight 
  from 
  the 
  South 
  

   Australian 
  species. 
  Additional 
  material 
  is 
  needed 
  to 
  accurately 
  fix 
  

   the 
  status 
  of 
  these 
  forms, 
  but 
  there 
  is 
  little 
  doubt 
  this 
  shell 
  is 
  

   specifically 
  distinct. 
  

  

  III. 
  Geographical 
  Notes. 
  

  

  AVe 
  have 
  previously 
  noted 
  the 
  importance 
  of 
  the 
  Chiton 
  fauna 
  of 
  

   Australia 
  in 
  connexion 
  with 
  zoogeographical 
  px'oblems, 
  and 
  have 
  

   cited 
  them 
  in 
  support 
  of 
  Hedley's 
  theory 
  of 
  the 
  Bassian 
  Isthmus. 
  

   The 
  results 
  of 
  the 
  present 
  study 
  are 
  striking 
  and 
  such 
  as 
  we 
  had 
  not 
  

  

  