﻿No. 
  1959. 
  SIPVNCULID8 
  OF 
  EASTERN 
  NORTH 
  AMERICA— 
  GEROULD. 
  427 
  

  

  they 
  run 
  forward 
  toward 
  the 
  base 
  of 
  the 
  introvert. 
  The 
  posterior 
  

   shield 
  has 
  22-26 
  radial 
  furrows, 
  of 
  which 
  only 
  about 
  15 
  reach 
  the 
  

   rounded 
  elevation 
  at 
  the 
  center. 
  The 
  edges 
  of 
  the 
  posterior 
  shield, 
  

   by 
  the 
  contraction 
  of 
  the 
  circular 
  muscles 
  in 
  front 
  of 
  it, 
  sometimes 
  

   project 
  above 
  the 
  general 
  surface 
  of 
  the 
  body, 
  so 
  that 
  the 
  radially 
  

   ribbed, 
  circular 
  shield, 
  rising 
  like 
  a 
  flat 
  dome 
  from 
  the 
  cylindrical 
  

   trunk 
  in 
  a 
  contracted 
  specimen, 
  suggests 
  an 
  extremely 
  ornamental 
  

   roof 
  of 
  a 
  Chinese 
  pagoda. 
  

  

  The 
  longitudinal 
  muscle 
  layer 
  consists 
  of 
  about 
  46 
  flat, 
  plate-like 
  

   bands, 
  which 
  anastomose 
  under 
  the 
  anal 
  shield 
  and 
  in 
  the 
  region 
  of 
  

   the 
  nephridia. 
  The 
  single 
  retractor 
  muscle 
  formed 
  by 
  the 
  fusion 
  

   of 
  the 
  two 
  ventral 
  retractors 
  is 
  attached 
  to 
  the 
  body 
  wall 
  by 
  two 
  

   roots, 
  one 
  on 
  each 
  side 
  of 
  the 
  nerve 
  cord 
  at 
  a 
  considerable 
  distance 
  

   (= 
  two-sevenths 
  the 
  length 
  of 
  the 
  trunk) 
  in 
  front 
  of 
  the 
  posterior 
  

   shield. 
  

  

  A 
  prominent 
  transverse 
  septum 
  stretches 
  across 
  the 
  coelom 
  imme- 
  

   diately 
  in 
  front 
  of 
  the 
  anus 
  and 
  the 
  openings 
  of 
  the 
  nephridia, 
  thus 
  

   isolating 
  a 
  small 
  space 
  beneath 
  the 
  anterior 
  shield. 
  

   The 
  nephridia 
  are 
  not 
  connected 
  with 
  it. 
  They 
  are 
  

   each 
  attached 
  to 
  the 
  body 
  wall 
  by 
  a 
  short 
  fold 
  of 
  peri- 
  

   toneum 
  extending 
  along 
  about 
  one-fifth 
  or 
  one-fourth 
  

   of 
  the 
  length 
  of 
  the 
  nephridium. 
  The 
  nephrostome 
  

   is 
  a 
  prominent 
  fold 
  with 
  a 
  heart-shaped 
  contour 
  con- 
  

   nected 
  with 
  the 
  rest 
  of 
  the 
  nephridium 
  by 
  a 
  slender 
  from^intro^- 
  

   neck. 
  The 
  intestinal 
  coil 
  of 
  many 
  whorls 
  is 
  held 
  to 
  '^^^'^ 
  °^ 
  ^^p^- 
  

   the 
  middle 
  of 
  the 
  posterior 
  shield 
  bj'' 
  a 
  large 
  columel- 
  ciosus. 
  x29o! 
  

   lar 
  muscle. 
  There 
  is 
  a 
  large, 
  oval 
  diverticulum 
  upon 
  

   the 
  rectum 
  near 
  the 
  anus. 
  The 
  rectum 
  is 
  held 
  by 
  a 
  longitudinal 
  

   fold 
  of 
  peritoneum 
  containing 
  muscle 
  fibers. 
  

  

  This 
  species 
  resembles 
  A. 
  Jclunzingeri 
  Selenka 
  and 
  Biilow 
  from 
  the 
  

   Red 
  Sea. 
  

  

  Genus 
  SIPUNCULUS 
  Linnseus. 
  

  

  This 
  genus 
  includes, 
  in 
  general, 
  large 
  sipunculids, 
  which 
  are 
  found 
  

   in 
  all 
  seas 
  from 
  the 
  polar 
  to 
  the 
  equatorial 
  regions. 
  The 
  trunk 
  is 
  

   without 
  papillse 
  and 
  the 
  introvert 
  without 
  hooks. 
  A 
  flat 
  tentacular 
  

   fold 
  surrounds 
  the 
  mouth, 
  and 
  its 
  margins 
  in 
  some 
  species 
  are 
  drawn 
  

   out 
  to 
  form 
  more 
  or 
  less 
  distinct 
  tentacles. 
  The 
  individual 
  tentacles 
  

   contain 
  a 
  network 
  of 
  blood 
  vessels 
  and 
  not 
  three 
  longitudinal 
  pas- 
  

   sages 
  as 
  in 
  Phascolosoma. 
  A 
  median-dorsal 
  unpaired 
  epithelial 
  tube 
  

   opens 
  upon 
  the 
  surface 
  of 
  the 
  head 
  immediately 
  behind 
  the 
  tentacu- 
  

   lar 
  fold, 
  and 
  leads 
  backward 
  to 
  a 
  cerebral 
  sense 
  organ 
  anterior 
  and 
  

   ventral 
  to 
  the 
  brain. 
  The 
  esophageal 
  connectives 
  do 
  not 
  surround 
  

   the 
  attachments 
  of 
  the 
  retractor 
  muscles 
  to 
  the 
  head, 
  as 
  in 
  most 
  

   sipunculids, 
  but 
  lie 
  behind 
  and 
  beneath 
  these 
  attachments. 
  There 
  

   are 
  usually 
  two 
  contractile 
  tubes 
  of 
  the 
  vascular 
  system. 
  One 
  or 
  

  

  