﻿NO. 
  1959. 
  8IPVNCULIDS 
  OF 
  EASTERN 
  NORTH 
  AMERICA— 
  OEROULD. 
  413 
  

  

  mens 
  of 
  this 
  form 
  has 
  convmced 
  me 
  that 
  it 
  is 
  to 
  be 
  regarded 
  as 
  

   merely 
  an 
  unstable 
  variety 
  of 
  a 
  very 
  plastic 
  species. 
  

  

  Although 
  it 
  is 
  exceedingly 
  difficult 
  to 
  estimate 
  accurately 
  the 
  

   length 
  of 
  the 
  introvert 
  in 
  specimens 
  preserved 
  in 
  all 
  states 
  of 
  con- 
  

   traction, 
  there 
  seems 
  to 
  be 
  no 
  room 
  for 
  doubt 
  that 
  even 
  in 
  the 
  same 
  

   region 
  off 
  Nova 
  Scotia 
  a 
  form 
  with 
  an 
  introvert 
  shorter 
  than 
  the 
  

   trunk 
  is 
  found 
  along 
  with 
  the 
  common 
  type. 
  This 
  may 
  be 
  due 
  in 
  

   part 
  to 
  the 
  fact 
  that 
  these 
  individuals 
  inhabit 
  tubes 
  of 
  Pectinaria 
  

   or 
  of 
  Hyalincecia 
  or 
  the 
  shells 
  of 
  Dentalium, 
  which 
  elongates 
  the 
  

   trunk 
  by 
  compression, 
  and 
  moreover 
  makes 
  the 
  skin 
  in 
  the 
  region 
  of 
  

   the 
  holdfasts 
  lustrous. 
  

  

  Another 
  peculiarity 
  to 
  which 
  I 
  was 
  at 
  first 
  inclined 
  to 
  attach 
  

   much 
  importance 
  is 
  the 
  fact 
  that 
  the 
  specimens 
  from 
  certain 
  locali- 
  

   ties 
  near 
  Halifax 
  either 
  have 
  the 
  dorsal 
  retractor 
  muscle 
  slightly 
  

   divided 
  at 
  the 
  base, 
  or 
  else 
  it 
  readily 
  separates 
  into 
  two 
  parts 
  in 
  

   making 
  a 
  dissection. 
  This, 
  however, 
  is 
  not 
  a 
  constant 
  character. 
  

   Specimens 
  from 
  the 
  same 
  region 
  in 
  most 
  cases 
  have 
  an 
  undivided 
  

   dorsal 
  retractor. 
  

  

  These 
  peculiarities, 
  although 
  not 
  of 
  sufficient 
  importance 
  to 
  estabHsh 
  

   a 
  distinct 
  species, 
  do 
  mark 
  the 
  presence 
  of 
  a 
  tendency 
  which 
  may 
  be 
  

   expressed 
  as 
  a 
  variety 
  or 
  strain, 
  which 
  may 
  be 
  called 
  canadensis, 
  the 
  

   characteristics 
  of 
  which 
  may 
  be 
  briefly 
  summarized 
  as 
  follows, 
  though 
  

   it 
  should 
  be 
  noted 
  that 
  there 
  is 
  such 
  a 
  mixture 
  constantly 
  occurring 
  

   between 
  this 
  and 
  the 
  typical 
  variety, 
  fusca, 
  as 
  to 
  make 
  it 
  impos- 
  

   sible 
  in 
  some 
  instances 
  to 
  make 
  these 
  distinctions: 
  Introvert 
  from 
  

   one-third 
  to 
  one-half 
  the 
  length 
  of 
  the 
  trunk 
  in 
  extreme 
  cases, 
  but 
  

   in 
  other 
  individuals 
  equal 
  in 
  length 
  to 
  the 
  trunk. 
  The 
  skin 
  is 
  smooth, 
  

   except 
  for 
  prominent 
  papillae 
  near 
  the 
  base 
  of 
  the 
  introvert 
  which 
  

   are 
  oval, 
  with 
  a 
  small, 
  nipple-shaped 
  tip, 
  or 
  cylindrical. 
  Minute, 
  

   slender, 
  conical 
  papillae 
  are 
  found 
  at 
  the 
  posterior 
  end 
  of 
  the 
  body. 
  

   The 
  region 
  covered 
  with 
  holdfasts 
  is 
  smooth, 
  lustrous, 
  and 
  often 
  

   iridescent; 
  this 
  region 
  extends 
  forward 
  as 
  far 
  as 
  the 
  middle 
  third 
  

   of 
  the 
  trunk, 
  which 
  is 
  covered 
  with 
  very 
  minute 
  papillae 
  but 
  other- 
  

   wise 
  smooth. 
  The 
  dorsal 
  retractor 
  is 
  distinctly 
  divided 
  at 
  its 
  attach- 
  

   ment 
  to 
  the 
  body 
  wall 
  at 
  the 
  posterior 
  end 
  of 
  the 
  trunk. 
  There 
  is 
  

   less 
  difference 
  in 
  size 
  between 
  the 
  dorsal 
  and 
  ventral 
  retractors 
  than 
  

   in 
  the 
  typical 
  variety. 
  The 
  nephridium 
  in 
  this 
  form 
  is 
  relatively 
  

   short, 
  and 
  the 
  nephrostome, 
  as 
  in 
  the 
  variet}' 
  gracilis, 
  has 
  a 
  slender 
  

   neck. 
  

  

  PHASCOLION 
  STROMBI 
  var. 
  L^ffiVIS, 
  new 
  variety. 
  

  

  Station 
  160, 
  5 
  miles 
  off 
  Thatchers 
  Island, 
  in 
  54 
  fathoms. 
  

  

  Type.— 
  Ceit. 
  No. 
  15109, 
  U.S.N.M. 
  

  

  This 
  variety, 
  which 
  I 
  was 
  at 
  first 
  inclined 
  to 
  regard 
  as 
  a 
  distinct 
  

   species, 
  lives 
  in 
  tubes 
  constructed 
  of 
  fine 
  pebbles 
  of 
  different 
  sizes 
  

   firmly 
  cemented 
  together 
  and 
  consisting 
  of 
  two 
  parts, 
  namely, 
  that 
  

  

  