﻿414 
  

  

  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  tol. 
  44. 
  

  

  covering 
  the 
  tnink, 
  similar 
  to 
  the 
  tubo 
  of 
  the 
  variety 
  tuhicola, 
  and 
  a 
  

   slenderer, 
  extremely 
  long, 
  tapering 
  portion 
  that 
  covers 
  the 
  introvert. 
  

   The 
  latter 
  part 
  of 
  the 
  tube, 
  like 
  the 
  former, 
  contains 
  minute 
  pebbles 
  

   and 
  particles 
  of 
  mud 
  that 
  are 
  graduated 
  in 
  size, 
  becoming 
  finer 
  

   toward 
  the 
  distal 
  end 
  and 
  embedded 
  in 
  a 
  parchment-like 
  material, 
  

   which 
  alone 
  forms 
  the 
  small 
  anterior 
  extremity 
  of 
  the 
  tube. 
  

  

  This 
  variety, 
  of 
  which 
  I 
  have 
  examined 
  only 
  one 
  complete 
  speci- 
  

   men, 
  is 
  characterized 
  externally 
  by 
  having 
  an 
  unusually 
  long, 
  slender, 
  

   smooth, 
  and 
  light-colored 
  introvert 
  (pi. 
  60, 
  fig. 
  13) 
  that 
  is 
  somewhat 
  

  

  sharply 
  marked 
  off 
  from 
  the 
  thicker, 
  

   darker-colored 
  trunk, 
  which 
  at 
  the 
  

   posterior 
  end 
  is 
  sharply 
  truncated 
  

   and 
  of 
  a 
  light 
  brown 
  color. 
  

  

  The 
  length 
  of 
  the 
  trunk 
  of 
  the 
  

   single 
  entire 
  specimen 
  is 
  about 
  6^ 
  

   mm. 
  ; 
  the 
  introvert 
  is 
  about 
  twice 
  as 
  

   long; 
  the 
  greatest 
  diameter 
  of 
  the 
  

   trunk 
  is 
  about 
  2 
  mm., 
  of 
  the 
  introvert 
  

   about 
  seven-eighths 
  mm. 
  The 
  pa- 
  

   pillae 
  of 
  the 
  anterior 
  part 
  of 
  the 
  trunk 
  

   are 
  small, 
  inconspicuous, 
  oval 
  eleva- 
  

   tions; 
  and 
  the 
  rest 
  of 
  the 
  trunk 
  is 
  

   almost 
  smooth, 
  except 
  that 
  minute 
  

   epidermal 
  organs 
  are 
  scattered 
  over 
  

   the 
  region 
  immediately 
  in 
  front 
  of 
  the 
  

   extremely 
  small, 
  crescentic 
  holdfasts 
  

   which 
  occupy 
  a 
  zone 
  ver}'- 
  near 
  the 
  

   posterior 
  end 
  of 
  the 
  body. 
  

  

  The 
  introvert 
  is 
  smooth, 
  except 
  

   that 
  minute 
  papllae 
  are 
  scattered 
  

   over 
  its 
  posterior 
  third. 
  

  

  The 
  longitudinal 
  muscle 
  layer 
  is 
  

   continuous 
  and 
  lustrous. 
  The 
  dorsal 
  

   retractor 
  muscle 
  (fig. 
  11) 
  is 
  much 
  

   larger 
  than 
  the 
  ventral, 
  and 
  is 
  at- 
  

   tached 
  at 
  the 
  posterior 
  end 
  of 
  the 
  

   ccslom 
  by 
  two 
  widely 
  separate 
  roots,^each 
  with 
  a 
  broad 
  attachment. 
  

   The 
  two 
  roots 
  of 
  the 
  dorsal 
  muscle 
  unite 
  at 
  a 
  distance 
  from 
  the 
  

  

  .Ttr.d 
  

  

  Fig. 
  11.— 
  Dissection 
  of 
  Phascolion 
  

  

  STEOMBI 
  VAR. 
  L^VIS. 
  X 
  fi- 
  an, 
  ANUS; 
  

   m, 
  SUSPENSOKY 
  MUSCLE 
  OF 
  INTESTINE; 
  

  

  m. 
  rtr. 
  d, 
  dorsal 
  retractor 
  muscle; 
  

   m. 
  Ttr. 
  V, 
  ventral 
  retractor 
  muscle; 
  

   ne.ph, 
  nephridium; 
  n.v, 
  ventral 
  

   nerve 
  cord. 
  

  

  1 
  since 
  making 
  the 
  dissection 
  on 
  which 
  this 
  description 
  was 
  based, 
  I 
  have 
  frequently 
  found 
  that 
  in 
  cer- 
  

   tain 
  individuals 
  of 
  Ph.strombi 
  there 
  is 
  a 
  marked 
  tendency 
  for 
  a 
  really 
  undivided 
  dorsal 
  retractor 
  to 
  split 
  in 
  

   two 
  at 
  the 
  base 
  under 
  the 
  slightest 
  stress, 
  so 
  that 
  in 
  dissection 
  it 
  is 
  difTicult 
  to 
  ascertain 
  whether 
  the 
  dorsal 
  

   retractor 
  is 
  actually 
  divided 
  or 
  single. 
  Hence 
  too 
  much 
  taxonomic 
  weight 
  must 
  not 
  be 
  placed 
  upon 
  this 
  

   anatomical 
  difference. 
  Accordingly, 
  with 
  the 
  small 
  amount 
  of 
  material 
  at 
  hand, 
  I 
  am 
  inclined, 
  Qnally, 
  

   to 
  describe 
  tliis 
  form 
  as 
  a 
  variety 
  of 
  Ph. 
  strombi, 
  though 
  the 
  tube 
  which 
  it 
  constructs 
  and 
  its 
  long, 
  smooth 
  

   introvert, 
  not 
  to 
  mention 
  the 
  dorsal 
  retractor 
  muscles, 
  are 
  distinctly 
  paculiar; 
  for 
  Ph. 
  strombi, 
  particu- 
  

   larly 
  of 
  the 
  tubo-making 
  variety, 
  is 
  very 
  common 
  in 
  the 
  region 
  where 
  this 
  specimen 
  was 
  found, 
  and 
  it 
  

   would 
  be 
  expected 
  that 
  aberrations 
  or 
  mutations 
  would 
  occur, 
  and 
  it 
  is 
  such 
  that 
  I 
  believe 
  Ph. 
  strorvhi 
  

   var. 
  Istvii 
  to 
  be. 
  

  

  