﻿106 
  TROCEEDINGIS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  colorationhassiiggested 
  the 
  specific 
  name, 
  but 
  some 
  colour-aberrations 
  

   occur 
  in 
  wldoh 
  the 
  green 
  is 
  lacking, 
  being 
  pale 
  cream 
  splashed 
  with 
  

   Avbite 
  and 
  orange, 
  though 
  green 
  even 
  here 
  sometimes 
  recurs. 
  The 
  

   following 
  description 
  of 
  the 
  sculpture 
  is 
  drawn 
  up 
  from 
  a 
  perfectly 
  

   normal 
  specimen 
  of 
  small 
  size 
  selected 
  as 
  the 
  type. 
  

  

  Anterior 
  valve 
  regularly 
  radially 
  ribbed 
  with 
  about 
  fifty 
  flattened 
  

   ribs. 
  Median 
  valves 
  have 
  six 
  to 
  eight 
  similar 
  ribs 
  on 
  the 
  lateral 
  

   areas 
  ; 
  the 
  pleural 
  areas 
  have 
  a 
  few 
  longitudinal 
  wrinkled 
  threads 
  

   near 
  outer 
  edge 
  of 
  the 
  pleura, 
  the 
  rest 
  of 
  the 
  pleura 
  and 
  jugum 
  

   covered 
  with 
  fine 
  zigzag 
  wrinkled 
  lines. 
  Posterior 
  valve 
  regular 
  

   and 
  normal 
  ; 
  mucro 
  elevated 
  about 
  anterior 
  third 
  ; 
  sculpture 
  of 
  

   posterior 
  half 
  like 
  that 
  of 
  the 
  anterior 
  valve 
  ; 
  anterior 
  portion 
  

   sculptured 
  like 
  the 
  pleura. 
  Variation 
  in 
  the 
  sculpture 
  occurs 
  

   according 
  to 
  age 
  in 
  that 
  the 
  ribbing 
  on 
  the 
  anterior 
  valve 
  and 
  lateral 
  

   areas 
  of 
  median 
  valves 
  increases 
  through 
  divarication 
  and 
  also 
  tends 
  

   to 
  degenerate 
  into 
  nodules 
  through 
  the 
  intersection 
  of 
  the 
  concentric 
  

   growth-lines. 
  The 
  posterior 
  area 
  of 
  the 
  tail-valve 
  shows 
  this 
  more 
  

   strongly, 
  appeai'ing 
  in 
  some 
  cases 
  coarsely 
  nodulose. 
  Further 
  with 
  

   age, 
  the 
  pleural 
  sculpture 
  becomes 
  finer 
  and 
  the 
  zigzags 
  predominate. 
  

   Gii'dle-scales 
  distinctive 
  ; 
  near 
  the 
  shell 
  small 
  pointed 
  or 
  tending 
  to 
  

   mucronate 
  scales 
  bearing 
  striae, 
  and 
  comparatively 
  regular 
  for 
  about 
  

   half 
  the 
  width 
  of 
  the 
  rather 
  broad 
  girdle 
  ; 
  the 
  outer 
  half 
  covered 
  

   with 
  minute 
  scales, 
  irregular 
  atid 
  somewhat 
  varying 
  in 
  size. 
  

  

  Length 
  of 
  type 
  30 
  mm., 
  breadth 
  16 
  mm. 
  Dried 
  shell. 
  Length 
  

   of 
  largest 
  specimen 
  (dried) 
  49 
  mm., 
  breadth 
  24 
  mm. 
  

  

  The 
  series 
  examined 
  shows 
  two 
  phases, 
  a 
  lower 
  broader 
  shell 
  and 
  

   a 
  higher 
  narrower 
  shell 
  ; 
  they 
  are 
  certainly 
  conspecific 
  as 
  far 
  as 
  can. 
  

   be 
  determined 
  at 
  the 
  present 
  time, 
  and 
  the 
  only 
  suggestion 
  we 
  can 
  

   make 
  is 
  that 
  the 
  differences 
  may 
  be 
  sexual. 
  This 
  suggestion 
  is 
  being 
  

   investigated 
  as 
  it 
  may 
  explain 
  the 
  discrepancies 
  observed 
  in 
  otiicr 
  

   cases. 
  The 
  internal 
  structure 
  is 
  quite 
  normal, 
  the 
  coloration 
  varying 
  

   slightly 
  as 
  the 
  outer 
  coloration 
  varies. 
  

  

  Type 
  from 
  Port 
  Arthur, 
  southern 
  Tasmania, 
  collected 
  by 
  E. 
  Mawle. 
  

   llange, 
  east 
  and 
  south 
  coasts 
  of 
  Tasmania. 
  Swansea, 
  Kelvedon 
  

   (W. 
  L. 
  May) 
  ; 
  Port 
  Arthur 
  (W. 
  Torr, 
  W. 
  L. 
  May, 
  E. 
  Mawle). 
  

  

  9. 
  Chiton 
  contractus, 
  Reeve. 
  

  

  The 
  locality 
  given 
  when 
  this 
  species 
  was 
  described 
  was 
  "New 
  

   Zealand 
  ". 
  When 
  Pilsbry 
  dealt 
  with 
  it 
  (Man. 
  Conch., 
  vol. 
  xiv, 
  1892, 
  

   p. 
  93) 
  he 
  did 
  not 
  comment 
  upon 
  this, 
  but 
  simply 
  gave 
  " 
  Tasmania 
  

   (Mus. 
  Cuming.)". 
  This 
  was 
  taken 
  from 
  Carpenter's 
  Manuscript, 
  the 
  

   quotation 
  reading, 
  "There 
  are 
  3 
  specimens 
  in 
  the 
  Cuming 
  collection, 
  

   from 
  Tasmania, 
  and 
  two 
  on 
  the 
  same 
  tablet 
  which 
  are 
  really 
  an 
  

   intermediate 
  variety 
  of 
  /. 
  castus." 
  As 
  synonyms, 
  also 
  following 
  

   Carpenter, 
  Pilsbry 
  added 
  Chiton 
  decussatus, 
  E,eeve, 
  Chiton 
  cadus, 
  

   lleeve, 
  and 
  Lepidopleurus 
  speciosui, 
  H. 
  Ad. 
  & 
  Angas. 
  Later, 
  in 
  the 
  

   Nautilus, 
  vol. 
  viii, 
  p. 
  129, 
  March, 
  1895, 
  Pilsbry 
  recorded, 
  " 
  By 
  the 
  

   study 
  of 
  many 
  specimens 
  received 
  from 
  Messrs. 
  Bednall 
  & 
  Cox, 
  1 
  find 
  

   that 
  two 
  species 
  were 
  ' 
  lumped 
  ' 
  under 
  the 
  name 
  Ischnochiton 
  

   contractics. 
  (1) 
  /. 
  decussatus, 
  lleeve, 
  of 
  which 
  castus, 
  lieeve, 
  and 
  

  

  