﻿ECHTNODERMATA. 
  135 
  

  

  Diameter 
  of 
  disk 
  19 
  millim., 
  length 
  of 
  arm 
  about 
  83 
  millim. 
  from 
  

   the 
  edge 
  of 
  the 
  disk, 
  width 
  of 
  arm 
  at 
  disk 
  6 
  millim., 
  height 
  of 
  same 
  

   5 
  millim. 
  Fourteen 
  mouth-papillse 
  of 
  fair 
  size, 
  the 
  outermost 
  the 
  

   largest 
  ; 
  four 
  stout 
  teeth 
  ; 
  mouth-plates 
  with 
  six 
  sides, 
  the 
  ahoral 
  

   the 
  longest 
  and 
  the 
  adoral 
  the 
  shortest, 
  longest 
  hardly 
  longer 
  than 
  

   broadest 
  axis 
  ; 
  accessory 
  mouth-plates 
  large, 
  longer 
  than 
  broad, 
  

   straight 
  within, 
  convex 
  without; 
  side 
  mouth-shields 
  distinct, 
  in- 
  

   clined 
  to 
  be 
  triangular, 
  broader 
  within 
  than 
  without 
  ; 
  granulated 
  

   space 
  between 
  mouth-papillaj 
  and 
  mouth-shield 
  very 
  small. 
  

  

  Lower 
  arm-plates 
  at 
  first 
  wider 
  than 
  long, 
  but 
  varying 
  a 
  good 
  

   deal 
  in 
  shape 
  ; 
  proceeding 
  outwards 
  the 
  adoral 
  edge 
  becomes 
  shorter 
  

   and 
  shorter 
  as 
  the 
  side 
  arm-plates 
  encroach 
  more 
  and 
  more 
  upon 
  the 
  

   ventral 
  middle 
  line. 
  The 
  upper 
  arm-plates 
  at 
  the 
  base 
  of 
  the 
  arms 
  

   are 
  very 
  wide, 
  about 
  foui* 
  times 
  as 
  wide 
  as 
  they 
  are 
  long, 
  further 
  

   out 
  they 
  become 
  narrower, 
  and 
  towards 
  the 
  tip 
  of 
  the 
  arm 
  are 
  very 
  

   much 
  encroached 
  upon 
  by 
  the 
  side 
  plates 
  ; 
  as 
  a 
  rule 
  there 
  are 
  seven 
  

   spines 
  ou 
  the 
  plates. 
  Tentacle-scales 
  two. 
  

  

  This 
  fine 
  form 
  stands 
  nearest 
  to 
  P. 
  marmorata, 
  from 
  which 
  it 
  

   may 
  be 
  distinguished 
  by 
  (i.) 
  the 
  much 
  larger 
  radial 
  shields, 
  (ii.) 
  the 
  

   wider 
  arm-bases, 
  (iii.) 
  smaller 
  number 
  of 
  arm-spines, 
  (iv.) 
  larger 
  

   accessory 
  mouth-shield, 
  and 
  (v.) 
  proportionately 
  shorter 
  arms. 
  

  

  Port 
  Molle 
  (14 
  fms.). 
  

  

  OPHIOPINAX, 
  g. 
  n. 
  

  

  It 
  appears 
  to 
  be 
  necessary 
  to 
  establish 
  a 
  new 
  genus 
  for 
  the 
  re- 
  

   ception 
  of 
  the 
  form 
  hitherto 
  known 
  as 
  Pectinura 
  steUata, 
  owing 
  to 
  

   the 
  remarkable 
  and 
  regular 
  arrangement 
  of 
  the 
  large 
  plates 
  on 
  its 
  

   disk 
  ; 
  this, 
  which 
  is 
  only 
  obscurely 
  seen 
  in 
  smaller 
  specimens, 
  be- 
  

   comes 
  very 
  prominent 
  in 
  such 
  larger 
  examples 
  as 
  were 
  obtained 
  

   during 
  the 
  voyage 
  of 
  the 
  ' 
  Alert.' 
  

  

  The 
  genus 
  may 
  be 
  defined 
  as 
  follows: 
  — 
  Two 
  elongated 
  genital 
  clefts; 
  

   mouth-papillse, 
  teeth. 
  Accessory 
  oral 
  shields 
  ; 
  arm-sijines 
  delicate, 
  

   attached 
  to 
  the 
  outer 
  edge 
  of 
  the 
  side 
  arm-plates. 
  Eadial 
  shields 
  

   large, 
  separated 
  by 
  several 
  radial 
  or 
  interradial 
  plates 
  from 
  one 
  

   another. 
  All 
  the 
  disk, 
  except 
  the 
  radial 
  shields, 
  is 
  covered 
  by 
  

   granules, 
  but 
  there 
  are 
  no 
  spines 
  or 
  spinous 
  processes. 
  Teeth 
  (in 
  

   four 
  rows) 
  stout, 
  blunt. 
  Side 
  arm-plates 
  extend 
  on 
  to 
  both 
  actinal 
  

   and 
  abactinal 
  surfaces 
  ; 
  side 
  mouth-shields 
  naked. 
  

  

  The 
  extraordinary 
  development 
  of 
  the 
  plates 
  between 
  the 
  radial 
  

   shields, 
  both 
  of 
  the 
  same 
  and 
  of 
  the 
  neighbouring 
  sets, 
  appears 
  to 
  

   have 
  escaped 
  the 
  notice 
  of 
  Ljungman 
  and 
  Grube 
  ; 
  nor 
  can 
  it, 
  I 
  

   imagine, 
  have 
  been 
  noticed 
  by 
  Mr, 
  Lyman, 
  as 
  he 
  retains 
  0. 
  stellata 
  

   of 
  Ljungman 
  in 
  the 
  emended 
  genus 
  Pectinura. 
  

  

  At 
  this 
  time 
  it 
  ajjpcars 
  convenient 
  to 
  redescribe 
  and 
  figure 
  the 
  

   species. 
  

  

  