﻿180 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  io3 
  

  

  when 
  the 
  animal 
  matures 
  completely. 
  The 
  ovaries 
  are 
  situated 
  

   behind 
  the 
  third 
  or 
  fourth 
  lateral 
  branch 
  of 
  the 
  anterior 
  iatestiual 
  

   trunk. 
  

  

  The 
  genital 
  pore 
  (pg) 
  leads 
  into 
  an 
  undivided 
  cavity, 
  the 
  genital 
  

   atrium 
  (a), 
  which 
  is 
  narrow 
  at 
  the 
  pore 
  and 
  expands 
  anteriorly. 
  The 
  

   narrow 
  posterior 
  part 
  receives 
  the 
  outlet 
  of 
  the 
  copulatory 
  bursa 
  and, 
  

   anteriorly 
  to 
  it, 
  the 
  opening 
  of 
  the 
  common 
  oviduct. 
  

  

  The 
  penis 
  has 
  a 
  fauiy 
  large, 
  spherical 
  bulb 
  and 
  a 
  plump 
  and 
  short 
  

   papilla. 
  The 
  bulb 
  contains 
  a 
  cavity 
  with 
  irregular 
  outline, 
  the 
  seminal 
  

   vesicle 
  (vs), 
  into 
  which 
  the 
  two 
  vasa 
  deferentia 
  (vd) 
  open 
  separately. 
  

   The 
  cavity 
  of 
  the 
  bulb 
  continues 
  into 
  the 
  broad 
  papUla 
  and 
  opens 
  at 
  

   its 
  tip. 
  The 
  bulb 
  has 
  the 
  usual 
  coat 
  of 
  muscle 
  fibers 
  arranged 
  in 
  

   concentric 
  layers. 
  The 
  papilla, 
  which 
  projects 
  only 
  little 
  into 
  the 
  

   genital 
  atrium, 
  has 
  two 
  muscle 
  layers 
  underlying 
  the 
  outer 
  epithelium, 
  

   a 
  circular 
  layer 
  and 
  a 
  longitudinal 
  one. 
  No 
  glandular 
  structures 
  are 
  

   differentiated 
  in 
  my 
  specimen. 
  

  

  The 
  two 
  oviducts 
  unite, 
  without 
  embracing 
  the 
  bursa 
  duct, 
  dorsally 
  

   to 
  the 
  genital 
  atrium. 
  The 
  common 
  oviduct 
  (ode) 
  opens 
  into 
  the 
  

   posterior, 
  narrow 
  part 
  of 
  the 
  atrium 
  from 
  the 
  dorsal 
  side. 
  

  

  The 
  bursa 
  (b) 
  is, 
  in 
  my 
  specimen, 
  a 
  rather 
  small 
  sac 
  with 
  a 
  narrow 
  

   lumen. 
  The 
  bursa 
  duct 
  (bd) 
  runs 
  posteriorly, 
  above 
  the 
  penis, 
  to 
  a 
  

   level 
  behind 
  the 
  genital 
  pore. 
  There 
  it 
  turns 
  abruptly 
  toward 
  the 
  

   ventral 
  side. 
  Its 
  terminal 
  portion 
  is 
  considerably 
  wider 
  than 
  the 
  

   anterior 
  part 
  of 
  the 
  duct 
  and 
  opens 
  from 
  the 
  posterodorsal 
  side 
  into 
  

   the 
  genital 
  atrium 
  close 
  to 
  the 
  genital 
  aperture. 
  In 
  full 
  maturity, 
  the 
  

   widened 
  section 
  of 
  the 
  bursa 
  duct 
  probably 
  represents 
  a 
  histologically 
  

   distinct 
  vagina. 
  

  

  Taxonomic 
  position. 
  — 
  The 
  systematic 
  relations 
  of 
  Dendrocoelopsis 
  

   alaskensis 
  are 
  discussed 
  together 
  with 
  those 
  of 
  the 
  preceding 
  species, 
  

   D. 
  piriformis. 
  D. 
  alaskensis 
  is 
  distinguished 
  from 
  all 
  other 
  species 
  

   of 
  the 
  genus 
  by 
  the 
  lack 
  of 
  a 
  grasping 
  organ. 
  

  

  Holotype. 
  On 
  seven 
  slides, 
  USNM 
  22335, 
  creek 
  crossing 
  Elliot 
  

   Highway 
  at 
  milepost 
  31.0, 
  July 
  24, 
  1950. 
  

  

  Distribution 
  and 
  ecology. 
  — 
  Dendrocoelopsis 
  alaskensis 
  is 
  an 
  inhabitant 
  

   of 
  cool, 
  fast 
  streams 
  of 
  the 
  White 
  Mountains 
  and 
  usually 
  shares 
  its 
  

   habitat 
  with 
  Phagocata 
  nivea. 
  It 
  is 
  a 
  stenothermic 
  and 
  rheophUic 
  

   species. 
  

  

  Clear 
  spring 
  and 
  creek 
  on 
  Steese 
  Highway, 
  milepost 
  82.5, 
  at 
  the 
  Alaska 
  Road 
  

   Commission 
  camp, 
  July 
  21, 
  1950; 
  one 
  immature 
  specimen, 
  under 
  a 
  stone. 
  

  

  Stream 
  crossing 
  Steese 
  Highway 
  at 
  milepost 
  84.0 
  (see 
  pi. 
  8), 
  altitude 
  2,700 
  

   feet, 
  July 
  21, 
  1950; 
  two 
  immature 
  specimens, 
  under 
  stones, 
  near 
  liver 
  bait. 
  

  

  Creek 
  crossing 
  Elliot 
  Highway 
  at 
  milepost 
  31.0, 
  July 
  24, 
  1950, 
  water 
  tempera- 
  

   ture 
  3.2° 
  C; 
  under 
  stones, 
  five 
  specimens, 
  two 
  of 
  them 
  with 
  sexual 
  structures 
  

   Giolotype) 
  . 
  

  

  