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  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  io3 
  

  

  In 
  Phagocata 
  nivea 
  the 
  penis 
  lumen 
  opens 
  usually 
  below 
  the 
  tip 
  of 
  

   the 
  penis 
  papilla. 
  This 
  character 
  has 
  been 
  used 
  by 
  Livanov 
  and 
  

   Zabusova 
  (1940, 
  p. 
  96) 
  to 
  segregate 
  a 
  group 
  of 
  Asiatic 
  species 
  from 
  

   Phagocata 
  and 
  to 
  place 
  them 
  in 
  a 
  new 
  genus, 
  Penecurva. 
  The 
  same 
  

   character 
  is 
  found, 
  however, 
  in 
  a 
  common 
  North 
  American 
  species, 
  

   Phagocata 
  morgani, 
  which 
  shows 
  no 
  other 
  close 
  relations 
  with 
  the 
  

   Asiatic 
  group. 
  This 
  character 
  is 
  apparently 
  inadequate 
  as 
  a 
  basis 
  

   for 
  the 
  establishment 
  of 
  a 
  new 
  genus. 
  

  

  Holotype. 
  — 
  On 
  one 
  slide, 
  USNM 
  22332, 
  creek 
  crossing 
  EUiot 
  High- 
  

   way 
  at 
  milepost 
  ^31.0, 
  July 
  24, 
  1950. 
  

  

  Distribution 
  and 
  ecology. 
  — 
  Phagocata 
  nivea 
  was 
  collected 
  in 
  cool, 
  

   fast 
  mountain 
  streams 
  on 
  the 
  slopes 
  of 
  the 
  White 
  Mountains, 
  a 
  range 
  

   north 
  of 
  Fairbanks. 
  The 
  temperature 
  of 
  the 
  water 
  ranged 
  from 
  3.2 
  

   to 
  7.2° 
  C. 
  (July). 
  The 
  animals 
  are 
  cold-stenothermic 
  and 
  do 
  not 
  

   tolerate 
  sudden 
  increases 
  in 
  temperature. 
  They 
  were 
  often 
  found 
  

   in 
  the 
  company 
  of 
  another 
  white 
  triclad, 
  Dendrocoelopsis 
  alaskensis. 
  

  

  Stream 
  on 
  Steese 
  Highway 
  (pi. 
  8), 
  at 
  milepost 
  84.0, 
  altitude 
  2,700 
  feet, 
  July 
  

   19 
  and 
  21, 
  1950, 
  water 
  temperature 
  6.9° 
  C; 
  one 
  immature 
  and 
  one 
  mature 
  speci- 
  

   men, 
  from 
  under 
  stones. 
  

  

  Willow 
  Creek, 
  on 
  Steese 
  Highway, 
  at 
  milepost 
  96.6, 
  altitude 
  2,100 
  feet, 
  July 
  

   19, 
  1950, 
  7.2° 
  C; 
  two 
  immature 
  specimens, 
  from 
  under 
  stones. 
  

  

  Spring 
  and 
  stream 
  on 
  Steese 
  Highway, 
  milepost 
  82.5, 
  near 
  Alaska 
  Road 
  Com- 
  

   mission 
  camp, 
  July 
  21, 
  1950; 
  two 
  mature 
  and 
  six 
  immature 
  specimens, 
  on 
  the 
  

   undersides 
  of 
  stones. 
  

  

  Fox 
  Gulch, 
  on 
  Elliot 
  Highway, 
  milepost 
  1.2, 
  July 
  24, 
  1950, 
  6.0° 
  C, 
  one 
  small 
  

   specimen 
  near 
  bait 
  (beef 
  liver). 
  

  

  Creek 
  crossing 
  Elliot 
  Highway 
  at 
  milepost 
  31.0, 
  July 
  24, 
  1950; 
  39 
  specimens, 
  

   about 
  half 
  of 
  them 
  mature, 
  collected 
  under 
  stones 
  (holotype). 
  

  

  Genus 
  Polycelis 
  Ehrenberg 
  

   Polycelis 
  borealis^ 
  new 
  species 
  

  

  Figure 
  22; 
  Plate 
  6, 
  Figure 
  2 
  

  

  Description. 
  — 
  Mature 
  animals 
  are 
  usually 
  12 
  to 
  15 
  mm. 
  long 
  and 
  

   1.5 
  to 
  2 
  mm. 
  wide 
  (larger 
  specimens, 
  measuring 
  up 
  to 
  20 
  mm. 
  in 
  

   length, 
  have 
  been 
  seen). 
  The 
  frontal 
  margin 
  is 
  slightly 
  convex. 
  At 
  

   the 
  lateral 
  corners 
  of 
  the 
  head 
  there 
  is 
  a 
  pair 
  of 
  elongated, 
  bluntly 
  

   pointed 
  auricles 
  which 
  are 
  held 
  raised 
  when 
  the 
  animal 
  is 
  gliding 
  

   quietly. 
  Behind 
  the 
  auricles, 
  the 
  body 
  first 
  narrows 
  slightly, 
  then 
  

   gradually 
  widens, 
  reaching 
  its 
  greatest 
  width 
  at 
  the 
  level 
  of 
  the 
  

   pharynx. 
  Behind 
  the 
  pharynx 
  the 
  body 
  tapers 
  to 
  a 
  moderately 
  

   pointed 
  posterior 
  end. 
  

  

  The 
  color 
  of 
  the 
  dorsal 
  side 
  is 
  usually 
  a 
  uniform 
  light 
  or 
  dark 
  

   brown, 
  that 
  of 
  the 
  ventral 
  side 
  a 
  light 
  grayish 
  brown. 
  In 
  animals 
  

  

  ' 
  The 
  large 
  highways 
  of 
  Alaska 
  are 
  marked 
  with 
  wooden 
  mileposts 
  indlcatmg 
  only 
  full 
  miles. 
  Many 
  

   posts 
  were 
  missing 
  at 
  the 
  time 
  when 
  the 
  collections 
  were 
  made. 
  Fractional 
  milages 
  were 
  usually 
  estimated 
  

   from 
  the 
  nearest 
  milepost 
  or 
  from 
  the 
  speedometer 
  readings 
  of 
  the 
  car 
  used. 
  

  

  