﻿M0LLU8CA. 
  83 
  

  

  115. 
  Chiton 
  (Macandrellus) 
  costatus. 
  (Plate 
  VI. 
  fig. 
  F.) 
  

  

  Acaiitliochites 
  costatus, 
  II. 
  Adams 
  *^- 
  Angas, 
  Froc. 
  Zoo/. 
  Soc. 
  1864, 
  

  

  p. 
  194 
  ; 
  Anffas, 
  I. 
  c. 
  1807, 
  p. 
  224. 
  

   Macaudrellus 
  costatus, 
  Z>«//, 
  i)"«//. 
  U.S. 
  Nat. 
  Mas. 
  i. 
  p. 
  81, 
  fig. 
  40 
  

  

  (dentition). 
  

  

  JIab. 
  Port 
  Jackson 
  {Angas 
  and 
  Coppinger). 
  

  

  The 
  single 
  specimen 
  before 
  me, 
  preserved 
  in 
  spirit, 
  shows 
  the 
  

   girdle 
  to 
  be 
  of 
  a 
  pale 
  buff 
  colour, 
  thick, 
  fleshy, 
  the 
  outer 
  margin 
  

   being 
  delicately 
  ciliated 
  with 
  a 
  minute 
  fringe 
  of 
  white 
  spicules. 
  

   The 
  tufts 
  of 
  spicules 
  arc 
  seven 
  in 
  number 
  along 
  each 
  side, 
  and 
  four 
  

   surrounding 
  the 
  front 
  valve. 
  The 
  middle 
  of 
  the 
  central 
  valves 
  is 
  

   occupied 
  by 
  a 
  raised, 
  transversely 
  substriated 
  flattened 
  ridge, 
  on 
  each 
  

   side 
  of 
  which 
  the 
  surface 
  is 
  granulated 
  or 
  rather 
  squamose, 
  the 
  

   scales 
  being 
  flat, 
  imbricating, 
  rather 
  large, 
  and 
  disposed 
  in 
  rather 
  

   regular 
  series. 
  The 
  lateral 
  areas 
  are 
  well 
  defined 
  by 
  a 
  raised 
  keel. 
  

   The 
  front 
  valve 
  has 
  five 
  radiating 
  costte, 
  and 
  apparently 
  the 
  same 
  

   number 
  of 
  slits 
  in 
  the 
  thin 
  lamina 
  of 
  insertion, 
  of 
  which 
  the 
  three 
  

   central 
  are 
  quite 
  distinct, 
  and 
  the 
  two 
  outer 
  ones 
  only 
  feebly 
  indi- 
  

   cated. 
  The 
  single 
  notch 
  on 
  each 
  side 
  the 
  intermediate 
  valves 
  is 
  

   also 
  very 
  slight. 
  The 
  posterior 
  valve 
  has 
  a 
  raised, 
  somewhat 
  ex- 
  

   centric 
  and 
  pointed 
  mucro, 
  from 
  which 
  six 
  more 
  or 
  less 
  distinct 
  

   radiating 
  ridges 
  descend 
  to 
  the 
  margin, 
  beneath 
  which 
  the 
  lamina 
  

   of 
  insertion 
  is 
  scalloped 
  by 
  a 
  similar 
  number 
  of 
  notches. 
  

  

  116. 
  Chiton 
  (Acanthochiton) 
  ashestoides. 
  (Plate 
  VI. 
  fig. 
  G.) 
  

  

  Shell 
  small, 
  greyish 
  brown, 
  with 
  a 
  pale 
  line 
  on 
  each 
  side 
  the 
  

   middle 
  of 
  the 
  central 
  valves, 
  slightly 
  converging 
  behind, 
  leaving 
  a 
  

   dark 
  wedge-shaped 
  space 
  between 
  them. 
  Surface 
  covered 
  with 
  a 
  

   coarsish 
  granulation, 
  the 
  granules 
  being 
  somewhat 
  flattened, 
  and 
  

   those 
  at 
  the 
  vertex 
  of 
  the 
  central 
  valves 
  rather 
  smaller 
  than 
  the 
  

   rest. 
  The 
  lateral 
  areas 
  are 
  not 
  defined 
  in 
  these 
  valves 
  ; 
  the 
  posterior 
  

   curved 
  margins 
  are 
  produced 
  in 
  the 
  middle, 
  at 
  times 
  almost 
  forming 
  

   a 
  right 
  angle 
  ; 
  their 
  insertion-plates 
  are 
  large, 
  thin, 
  produced 
  ante- 
  

   riorly, 
  with 
  a 
  very 
  slight 
  notch 
  quite 
  close 
  to 
  the 
  hinder 
  margin 
  on 
  

   each 
  side 
  ; 
  the 
  sinus 
  between 
  them 
  in 
  front 
  is 
  deep 
  and 
  arcuate. 
  

   The 
  first 
  valve 
  has 
  a 
  straighter 
  posterior 
  margin 
  than 
  the 
  succeed- 
  

   ing 
  ones, 
  and 
  a 
  semicircular 
  outline 
  in 
  front 
  ; 
  the 
  lamina 
  of 
  inser- 
  

   tion 
  is 
  rather 
  deep, 
  thin, 
  feebly 
  striated 
  exteriorly, 
  and 
  interrupted 
  

   by 
  five 
  very 
  small 
  subequidistant 
  notches. 
  The 
  last 
  valve 
  is 
  con- 
  

   spicuously 
  small, 
  transversely 
  subovate, 
  depressed-conical, 
  with 
  a 
  

   nearly 
  central 
  mucro 
  ; 
  insertion- 
  plate 
  very 
  large, 
  laterally 
  produced, 
  

   with 
  only 
  two 
  notches 
  behind. 
  Interior 
  of 
  the 
  valves 
  bluish. 
  

   Mantle 
  very 
  minutely 
  spinulose, 
  bearing 
  very 
  conspicuous 
  compact 
  

   tufts 
  of 
  silky 
  spicules 
  along 
  the 
  sides, 
  not 
  at 
  all 
  unlike 
  in 
  their 
  fibrous 
  

   texture 
  that 
  of 
  asbestos. 
  Length 
  15 
  millim., 
  width 
  of 
  the 
  broadest 
  

   central 
  valve 
  5|. 
  

  

  Hah. 
  Flinders 
  Island, 
  Bass's 
  Straits 
  {Joseph 
  MiUlgdn); 
  Port 
  

   Molle, 
  Queensland 
  [Coppint/cr). 
  

  

  g2 
  

  

  