﻿THE 
  ANATOJIY 
  OF 
  rfECII.OCHJiTUy, 
  CLAPAHEDE. 
  141 
  

  

  the 
  name 
  Trochocliseta 
  Sarsi 
  almost 
  certainly 
  belongs 
  to 
  

   Oersted's 
  species, 
  Disoma 
  multisetosuni. 
  

  

  Mesnil 
  (1897), 
  from 
  au 
  examination 
  of 
  the 
  type 
  specimens, 
  

   confirms 
  the 
  specific 
  identity 
  of 
  Michaelseu's 
  specimens 
  with 
  

   those 
  of 
  Oersted. 
  He 
  gives 
  some 
  further 
  details, 
  with 
  figures, 
  

   of 
  the 
  structure 
  of 
  the 
  worm, 
  and 
  expresses 
  tlie 
  opinion 
  

   that 
  Thaumastoma 
  singula 
  re, 
  described 
  by 
  Webster 
  and 
  

   Benedict 
  (1884, 
  p, 
  737), 
  from 
  the 
  American 
  coast, 
  is 
  the 
  

   same 
  species. 
  

  

  Claparede 
  (1868, 
  p. 
  337) 
  discussed 
  the 
  relations 
  of 
  Disoma 
  

   with 
  Poly 
  dor 
  a 
  and 
  with 
  Chtetopterus, 
  being 
  inclined 
  to 
  

   place 
  it 
  near 
  to 
  the 
  latter. 
  

  

  Levinseu 
  (1883, 
  p. 
  106) 
  pointed 
  out 
  that 
  the 
  two 
  genera, 
  

   Disoma 
  and 
  Poecilochsetus, 
  were 
  closely 
  related 
  to 
  each 
  

   other, 
  and 
  emphasised 
  their 
  resemblance 
  to 
  the 
  Spionidas. 
  

  

  Adopting 
  Levinsen's 
  view 
  of 
  the 
  relation 
  of 
  the 
  two 
  forms, 
  

   " 
  sans 
  avoir 
  pourtant 
  une 
  conviction 
  bieu 
  ferme," 
  Mesnil 
  

   (1897) 
  placed 
  both 
  in 
  his 
  family 
  Disomidas, 
  which 
  he 
  

   characterises 
  as 
  follows 
  : 
  

  

  Prostomium 
  very 
  simple, 
  with 
  two 
  long 
  tentacular 
  palps 
  

   analogous 
  to 
  those 
  of 
  the 
  Spionids. 
  Parapodia 
  biramous, 
  at 
  

   any 
  rate 
  in 
  the 
  anterior 
  region, 
  always 
  with 
  simple 
  bristles. 
  

   Bristles 
  of 
  various 
  kinds, 
  especially 
  large 
  spiny 
  bristles, 
  hairy 
  

   bristles, 
  and 
  large 
  lancet-shaped 
  bristles. 
  Stout 
  hooks 
  (soies 
  

   aciculaire) 
  in 
  the 
  neuropodia 
  of 
  segments 
  2, 
  3, 
  and 
  even 
  4. 
  

   Never 
  two 
  regions 
  of 
  the 
  body 
  clearly 
  marked 
  off. 
  Ventral 
  

   and 
  dorsal 
  cirri 
  elongate 
  or 
  fimbriate. 
  

  

  Mesnil 
  considers 
  this 
  family 
  as 
  intermediate 
  between 
  the 
  

   Spionidfe 
  and 
  Cha3topterid?e, 
  being 
  somewhat 
  nearer 
  to 
  the 
  

   latter. 
  He 
  also 
  points 
  out 
  that 
  in 
  certain 
  characters 
  the 
  two 
  

   genera 
  shoAv 
  some 
  affinities 
  with 
  the 
  Aphroditidaeand 
  Amplii- 
  

   nomidas, 
  and 
  that 
  this 
  is 
  particularly 
  true 
  of 
  Poecilochgetus 
  

   on 
  account 
  of 
  the 
  median 
  tentacle 
  and 
  tlie 
  large 
  spiny 
  bristles. 
  

   The 
  two 
  long 
  palps 
  and 
  the 
  tendency 
  of 
  the 
  first 
  segment 
  to 
  

   enclose 
  the 
  prostomium 
  also 
  point 
  in 
  the 
  same 
  direction. 
  

  

  My 
  OAvn 
  observations 
  on 
  Poecilochaetus 
  and 
  a 
  study 
  of 
  

   the 
  different 
  descriptions 
  of 
  Disoma 
  lead 
  me 
  to 
  agree 
  with 
  

  

  