﻿376 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  vol. 
  44. 
  

  

  In 
  shallow 
  water 
  are 
  found 
  Ph. 
  verriUii 
  (4-16 
  fathoms) 
  and 
  Ph. 
  

   cinereum 
  (45 
  fathoms). 
  Ph. 
  gouldii 
  (Pourtales) 
  and 
  Ph. 
  cylindraium 
  

   Keferstein 
  are 
  the 
  littoral 
  representatives 
  of 
  their 
  genus 
  upon 
  this 
  

   coast. 
  

  

  Sipunculus 
  nudus 
  Linnaeus 
  and 
  Siphonosoma 
  cumanense 
  (Keferstein) 
  

   var. 
  vitrea 
  are 
  both 
  littoral 
  species, 
  but 
  Sipunculus 
  priapuloides 
  

   Koren 
  and 
  Danielssen 
  is 
  found 
  in 
  478-1,069 
  fathoms. 
  

  

  Phascolion 
  stromhi 
  (Montagu) 
  occurs 
  at 
  all 
  depths 
  from 
  5 
  to 
  1,061 
  

   fathoms, 
  and 
  Ph. 
  alherti 
  Sluiter 
  at 
  depths 
  of 
  1,267-1,674 
  meters. 
  

  

  Physcosoma 
  varians 
  (Keferstein) 
  and 
  Ph. 
  antillarum 
  Grube 
  and 
  

   Orsted 
  are 
  littoral 
  forms, 
  but 
  Physcosoma 
  capitatum, 
  new 
  species, 
  

   inhabits 
  the 
  sea 
  bottom 
  at 
  677-1,769 
  fathoms. 
  

  

  Aspidosiphon 
  parvulus, 
  new 
  species, 
  occurs 
  in 
  16 
  fathoms; 
  A. 
  spe- 
  

   ciosus, 
  new 
  species, 
  is 
  found 
  in 
  the 
  coral 
  reefs 
  near 
  shore, 
  and 
  has 
  

   been 
  taken 
  also 
  at 
  a 
  depth 
  of 
  157 
  fathoms. 
  

  

  Dendrostoma 
  alutaceum 
  Grube 
  has 
  a 
  similar 
  distribution 
  among 
  

   coral 
  reefs 
  near 
  shore, 
  and 
  was 
  taken 
  off 
  Cape 
  Hatteras 
  at 
  a 
  depth 
  of 
  

   16 
  fathoms. 
  

  

  After 
  plotting 
  upon 
  a 
  map 
  the 
  principal 
  localities 
  at 
  which 
  sipun- 
  

   culids 
  occur 
  in 
  the 
  deeper 
  waters 
  off 
  our 
  coast 
  (p. 
  377), 
  I 
  was 
  inter- 
  

   ested 
  to 
  note 
  how 
  closely 
  they 
  follow 
  the 
  1,000-fathom 
  curve, 
  the 
  

   edge 
  of 
  the 
  continental 
  shelf. 
  This 
  is 
  probably 
  due 
  in 
  part 
  to 
  the 
  

   fact 
  that 
  dredging 
  operations 
  have 
  been 
  carried 
  on 
  more 
  extensively 
  

   along 
  this 
  belt 
  than 
  elsewhere, 
  but 
  may 
  it 
  not 
  possibly 
  indicate 
  that 
  

   the 
  conditions 
  there, 
  where 
  the 
  bottom 
  rapidly 
  descends 
  from 
  100 
  

   to 
  1,000 
  fathoms, 
  are 
  exceptionally 
  favorable 
  for 
  the 
  life 
  of 
  sipun- 
  

   culids? 
  Sipunculus 
  priapuloides, 
  Physcosoma 
  capitatum, 
  Phascolo- 
  

   soma 
  dnctum. 
  Ph. 
  procerum, 
  and 
  Ph. 
  margaritaceum 
  var. 
  meridionalis 
  

   have 
  been 
  found 
  only 
  along 
  this 
  edge 
  of 
  the 
  continental 
  shelf; 
  Ph. 
  

   eremita, 
  Ph. 
  sahellarise, 
  and 
  Ph. 
  improvisum 
  occur 
  not 
  only 
  there 
  but 
  

   in 
  shallower 
  waters 
  nearer 
  the 
  coast. 
  Phascolosoma 
  flagriferum 
  alone 
  

   occurs 
  beyond 
  the 
  1 
  ,000-fathom 
  line, 
  isolated 
  in 
  the 
  deep 
  sea. 
  

  

  Interrelationships 
  of 
  the 
  genera. 
  — 
  ^The 
  recognized 
  genera 
  of 
  sipuncu- 
  

   lids 
  are 
  so 
  closely 
  anastomosed 
  that 
  it 
  is 
  difficult 
  to 
  define 
  them 
  

   sharply 
  from 
  one 
  another. 
  For 
  example, 
  Ph. 
  gouldii, 
  which 
  is 
  clearly 
  

   a 
  species 
  of 
  Phascolosoma, 
  as 
  is 
  shown 
  by 
  its 
  tentacles, 
  integument, 
  

   arrangement 
  of 
  its 
  nervous 
  system, 
  and 
  its 
  development, 
  differs 
  from 
  

   all 
  other 
  species 
  of 
  Phascolosoma 
  and 
  resembles 
  all 
  known 
  species 
  of 
  

   Sipunculus 
  in 
  the 
  division 
  of 
  its 
  longitudinal 
  musculature 
  into 
  sepa- 
  

   rate 
  bands. 
  On 
  the 
  other 
  hand, 
  Physcosoma 
  capitatum, 
  new 
  species, 
  

   differs 
  from 
  all 
  other 
  known 
  species 
  of 
  that 
  genus 
  in 
  having 
  a 
  contin- 
  

   uous 
  layer 
  of 
  longitudinal 
  muscle 
  fibers, 
  and 
  in 
  this 
  respect 
  it 
  resem- 
  

   bles 
  the 
  Phascolosomas. 
  Yet 
  it 
  has 
  the 
  peculiar 
  form 
  of 
  head 
  and 
  

   crown 
  of 
  tentacles, 
  as 
  well 
  as 
  other 
  features 
  characteristic 
  of 
  the 
  

   genus 
  Physcosoma, 
  in 
  which 
  I 
  have 
  accordingly, 
  though 
  it 
  must 
  be 
  

  

  