﻿384 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  vol.44. 
  

  

  A 
  specimen 
  of 
  this 
  large 
  gray 
  PTiascolosoma 
  (pi. 
  58, 
  fig. 
  3) 
  was 
  

   dredged 
  at 
  each 
  of 
  the 
  above-mentioned 
  localities 
  off 
  Marthas 
  Vine- 
  

   yard 
  at 
  depths 
  from 
  100 
  to 
  266 
  fathoms. 
  In 
  all 
  respects 
  except 
  size 
  

   they 
  resemble 
  those 
  from 
  Bass 
  Kock 
  near 
  Edinburgh 
  described 
  by 
  

   Moebius, 
  but 
  the 
  largest 
  specimen 
  from 
  off 
  Marthas 
  Vineyard 
  is 
  

   five 
  times 
  the 
  length 
  of 
  those 
  from 
  the 
  North 
  Sea. 
  It 
  has 
  also 
  been 
  

   found 
  at 
  several 
  places 
  off 
  the 
  west 
  coast 
  of 
  Sweden, 
  according 
  to 
  

   Th^el 
  (1905), 
  at 
  depths 
  of 
  from 
  9 
  to 
  35 
  fathoms. 
  In 
  that 
  region 
  also 
  

   its 
  size 
  is 
  diminutive 
  compared 
  with 
  that 
  of 
  the 
  American 
  specimens. 
  

  

  Characteristics. 
  — 
  The 
  total 
  length 
  of 
  the 
  largest 
  individual 
  is 
  180 
  

   mm., 
  of 
  which 
  the 
  trunk 
  behind 
  the 
  anus 
  is 
  75 
  mm.; 
  thickness 
  of 
  the 
  

   trunk, 
  10 
  mm. 
  The 
  introvert 
  is 
  about 
  2| 
  times 
  as 
  long 
  as 
  the 
  trunk, 
  

   and 
  one-third 
  as 
  thick. 
  The 
  posterior 
  extremity 
  of 
  the 
  body 
  is 
  pro- 
  

   longed 
  into 
  a 
  slender, 
  tail-like 
  process, 
  which 
  in 
  one 
  specimen 
  is 
  about 
  

   half 
  as 
  long 
  as 
  the 
  thickness 
  of 
  the 
  trunk, 
  or 
  about 
  5 
  mm. 
  Color 
  

   gray, 
  the 
  introvert 
  of 
  one 
  specimen 
  being 
  slightly 
  iridescent. 
  The 
  

   cuticula 
  is 
  thrown 
  up 
  into 
  fine, 
  wavy 
  folds. 
  Both 
  trunk 
  and 
  intro- 
  

   vert 
  are 
  covered 
  sparsely 
  with 
  mmute, 
  dark-brown 
  papillse. 
  The 
  

   two 
  (ventral) 
  retractors 
  have 
  their 
  origui 
  at 
  the 
  extreme 
  posterior 
  

   end 
  of 
  the 
  body 
  (pi. 
  59, 
  fig. 
  8). 
  The 
  pair 
  of 
  nephridia 
  are 
  attached 
  

   slightly 
  in 
  front 
  of 
  the 
  anus, 
  and 
  hang 
  entirely 
  free. 
  Their 
  surface 
  

   is 
  slightly 
  rough. 
  The 
  esophagus 
  is 
  long; 
  the 
  rectum 
  very 
  short; 
  the 
  

   intestine 
  has 
  many 
  coils 
  closely 
  held 
  to 
  the 
  walls 
  of 
  the 
  body. 
  The 
  

   Pohan 
  tube 
  (contractile 
  vessel) 
  is 
  covered 
  with 
  branching 
  tufts 
  that 
  

   adhere 
  to 
  the 
  dorsal 
  wall 
  of 
  the 
  body. 
  

  

  A 
  notable 
  feature 
  of 
  the 
  nerve 
  cord 
  in 
  two 
  specimens 
  that 
  I 
  have 
  

   dissected 
  is 
  its 
  submergence 
  beneath 
  the 
  longitudinal 
  muscle 
  laj^er 
  

   near 
  the 
  posterior 
  end 
  of 
  the 
  body, 
  so 
  that 
  it 
  is 
  apparently 
  interrupted. 
  

   This 
  disappearance 
  begins 
  slightly 
  in 
  front 
  of 
  the 
  posterior 
  end 
  of 
  

   the 
  retractor 
  muscles 
  and 
  extends 
  forward 
  nearly 
  to 
  the 
  free 
  ends 
  of 
  

   the 
  nephridia. 
  The 
  retractors 
  in 
  this 
  region 
  are 
  closely 
  applied 
  to 
  

   the 
  layer 
  of 
  longitudinal 
  muscles, 
  and 
  united 
  with 
  them. 
  Theel's 
  

   (1905) 
  beautiful 
  figures 
  of 
  this 
  species 
  as 
  it 
  appears 
  off 
  the 
  west 
  coast 
  

   of 
  Sweden, 
  however, 
  show 
  that 
  the 
  fusion 
  of 
  the 
  retractor 
  muscles 
  to 
  

   the 
  body 
  wall 
  and 
  the 
  submergence 
  of 
  the 
  nerve 
  cord 
  beneath 
  the 
  

   longitudinal 
  muscles 
  near 
  the 
  posterior 
  end 
  of 
  the 
  body, 
  as 
  described 
  

   above, 
  are 
  not 
  characteristic 
  of 
  the 
  Swedish 
  and 
  North 
  Sea 
  representa- 
  

   tives 
  of 
  this 
  species, 
  and 
  it 
  is 
  perhaps 
  not 
  a 
  constant 
  characteristic 
  

   in 
  those 
  of 
  the 
  western 
  Atlantic. 
  

  

  According 
  to 
  Th6el 
  the 
  tentacles 
  are 
  arranged 
  in 
  six 
  groups, 
  varying 
  

   in 
  number 
  from 
  28 
  to 
  40. 
  The 
  skm 
  immediately 
  behmd 
  the 
  tentacles 
  

   is 
  thin 
  and 
  smooth, 
  not 
  covered 
  with 
  the 
  chitmous 
  cuticula 
  like 
  the 
  

   rest 
  of 
  the 
  body, 
  from 
  which 
  a 
  collar 
  or 
  fold 
  marks 
  off 
  this 
  smooth 
  zone. 
  

  

  