﻿ECHIJfODEEMATA. 
  137 
  

  

  plates 
  are 
  curved 
  ; 
  the 
  plates 
  themselves 
  are 
  at 
  first 
  broader 
  than 
  

   long, 
  but 
  during 
  their 
  gradual 
  diminution 
  in 
  size 
  they 
  have 
  at 
  one 
  

   time 
  their 
  aboral 
  edge 
  equal 
  to 
  their 
  longitudinal 
  axis 
  ; 
  still 
  further 
  

   out 
  they 
  are 
  longer 
  than 
  broad. 
  About 
  six, 
  short, 
  poorly 
  developed 
  

   spines 
  are 
  found 
  on 
  each 
  of 
  the 
  side 
  arm-plates 
  near 
  the 
  disk, 
  of 
  

   which 
  the 
  largest 
  are 
  median 
  in 
  position 
  ; 
  they 
  diminish 
  in 
  number 
  

   and 
  size 
  as 
  they 
  approach 
  the 
  free 
  end 
  of 
  the 
  arm. 
  Two 
  small 
  ten- 
  

   tacle-scales. 
  

  

  Upper 
  surface 
  (in 
  alcohol) 
  dark 
  yellow, 
  with 
  spots 
  or 
  patches 
  of 
  

   brown 
  ; 
  the 
  whole 
  of 
  the 
  actinal 
  surface 
  pale 
  flesh-colour. 
  Although, 
  

   as 
  a 
  rule, 
  three 
  consecutive 
  segments 
  are 
  coloured 
  by 
  a 
  darker 
  trans- 
  

   verse 
  patch, 
  there 
  may 
  be 
  only 
  two, 
  or 
  there 
  may 
  be 
  four 
  so 
  orna- 
  

   mented, 
  and, 
  as 
  irregularities, 
  one 
  or 
  more 
  than 
  four 
  ; 
  but 
  the 
  colo- 
  

   ration 
  always 
  extends 
  on 
  to 
  the 
  sides 
  of 
  the 
  arm, 
  though 
  it 
  never 
  

   passes 
  on 
  to 
  the 
  lower 
  surface. 
  Or 
  the 
  whole 
  may 
  be 
  very 
  many 
  

   shades 
  darker, 
  and 
  then 
  the 
  darkest 
  parts 
  are 
  not 
  especially 
  remark- 
  

   able 
  ; 
  this 
  last 
  mode 
  of 
  coloration 
  appears 
  to 
  be 
  by 
  far 
  the 
  most 
  

   comnion. 
  

  

  Port 
  Molle, 
  Queensland, 
  14 
  fms., 
  rock 
  ; 
  and 
  Port 
  Denison, 
  

   3-4 
  fms. 
  

  

  In 
  some 
  examples, 
  which 
  are 
  very 
  much 
  smaller, 
  from 
  Torres 
  Straits 
  

   the 
  radial 
  shields 
  are 
  oviform, 
  the 
  upper 
  arm-plates 
  are 
  not 
  nearly 
  

   so 
  wide 
  nor 
  so 
  distinctly 
  carinated 
  ; 
  the 
  central 
  rosette 
  may 
  be 
  only 
  

   barely 
  indicated, 
  though 
  the 
  central 
  plate 
  is 
  very 
  distinct 
  ; 
  the 
  plates 
  

   of 
  the 
  interradial 
  series 
  have 
  no 
  small 
  marginal 
  secondary 
  plates. 
  

   The 
  side 
  arm-plates 
  at 
  the 
  base 
  of 
  the 
  arm 
  are 
  proportionately 
  much 
  

   larger, 
  and 
  in 
  consequence 
  diminish 
  the 
  breadth 
  of 
  the 
  lower 
  as 
  well 
  

   as 
  of 
  the 
  upper 
  arm-plates. 
  Striking 
  as 
  is 
  the 
  difference 
  in 
  effect 
  

   produced 
  by 
  these 
  dift'erences 
  in 
  character, 
  they 
  are, 
  I 
  think, 
  only 
  

   to 
  be 
  ascribed 
  to 
  age. 
  

  

  5. 
  OpMopeza 
  conjimgens. 
  

  

  This 
  species 
  seems 
  to 
  strengthen 
  the 
  opinion, 
  more 
  than 
  once 
  ex- 
  

   pressed 
  by 
  Mr. 
  Lyman, 
  that 
  the 
  genera 
  O/ihiojJeza 
  and 
  Pectinura 
  are 
  

   barely 
  to 
  be 
  distinguished. 
  AVithout 
  a 
  divided 
  mouth-shield, 
  it 
  has 
  

   the 
  arms 
  not 
  rounded, 
  as 
  in 
  0. 
  fallcuv, 
  but 
  keeled 
  above, 
  as 
  is 
  so 
  often 
  

   the 
  case 
  in 
  Pectinura. 
  

  

  Most 
  closely 
  allied 
  to 
  0. 
  fallax, 
  it 
  may 
  be 
  distinguished 
  by 
  the 
  

   somewhat 
  coarser 
  granulation 
  of 
  its 
  disk, 
  the 
  smaller 
  number 
  of 
  

   mouth-papillse, 
  and 
  the 
  broadened 
  upper 
  arm-plates. 
  

  

  Disk 
  pentagonal, 
  flattened, 
  17'5 
  millim. 
  diam. 
  in 
  one 
  example, 
  

   completely 
  covered 
  by 
  a 
  delicate 
  and 
  regular 
  granulation 
  (of 
  about 
  

   twenty 
  granules 
  to 
  1 
  millim.), 
  the 
  underlying 
  scales 
  not 
  large 
  ; 
  the 
  

   radial 
  shields, 
  in 
  perfect 
  specimens, 
  only 
  indicated 
  by 
  depressions. 
  

   Mouth-shields 
  not 
  divided, 
  wider 
  than 
  long, 
  with 
  a 
  wide 
  convex 
  

   adoral 
  edge, 
  straighter 
  sides, 
  and 
  a 
  barely 
  convex 
  aboral 
  margin. 
  

   Side 
  mouth-shields 
  small 
  ; 
  the 
  space 
  between 
  the 
  mouth-shield 
  and 
  

   the 
  edge 
  of 
  the 
  jaws 
  is 
  marked 
  by 
  a 
  granulation, 
  much 
  coarser 
  than 
  

   that 
  which 
  obtains 
  elsewhere 
  on 
  the 
  disk. 
  Mouth-papillae 
  seven. 
  

  

  