﻿426 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Nymph. 
  Length 
  8 
  mm 
  ; 
  setae 
  4 
  mm 
  additional; 
  abdomen 
  4.5 
  mm 
  ; 
  

   antennae 
  1.5 
  mm. 
  

  

  Head 
  twice 
  as 
  wide 
  as 
  long 
  ; 
  thorax 
  convex 
  ; 
  legs 
  short 
  ; 
  tibia 
  about 
  

   equal 
  in 
  length 
  to 
  the 
  tarsus 
  without 
  its 
  claw; 
  abdomen 
  depressed, 
  

   widened 
  on 
  the 
  fourth 
  to 
  ninth 
  segments, 
  with 
  thin 
  lateral 
  margins, 
  pro- 
  

   duced 
  at 
  the 
  hind 
  angles 
  into 
  thin, 
  flat 
  teeth, 
  which 
  appear 
  in 
  outhne 
  

   like 
  the 
  teeth 
  of 
  a 
  circular 
  saw 
  ; 
  third 
  segment 
  with 
  a 
  minute 
  tooth, 
  first 
  

   and 
  second 
  segments 
  with 
  none 
  at 
  all, 
  loth 
  segment 
  with 
  a 
  low, 
  longi- 
  

   tudinal, 
  lateral 
  carina; 
  setae 
  fringed 
  in 
  the 
  middle, 
  nearly 
  naked 
  at 
  both 
  

   ends. 
  

  

  Color 
  dirty 
  yellowish, 
  darker 
  above, 
  paler 
  beneath. 
  

  

  Gills 
  double, 
  well 
  developed 
  on 
  the 
  fourth 
  to 
  the 
  sixth 
  segments, 
  rudi- 
  

   mentary 
  on 
  the 
  first 
  and 
  seventh, 
  and 
  absent 
  from 
  the 
  second 
  and 
  third 
  ; 
  

   the 
  opercular 
  anterior 
  leaf 
  on 
  the 
  fourth 
  segment 
  covers 
  all 
  the 
  gills 
  pos- 
  

   terior 
  to 
  it; 
  on 
  the 
  fifth 
  and 
  sixth 
  segments 
  the 
  anterior 
  leaf 
  is 
  similar 
  in 
  

   form 
  but 
  smaller 
  and 
  much 
  thinner 
  ; 
  the 
  delicate 
  posterior 
  leaf 
  on 
  the 
  

   fourth, 
  fifth 
  and 
  sixth 
  segments 
  is 
  two 
  parted 
  ; 
  on 
  the 
  first 
  segment 
  is 
  a 
  

   simple 
  cyhndric 
  rudiment, 
  jointed 
  on 
  a 
  low 
  pedicel 
  ; 
  on 
  the 
  seventh 
  

   segment 
  the 
  rudimentary 
  gill 
  is 
  leaflike, 
  single, 
  six 
  lobed. 
  

  

  July 
  19 
  quite 
  a 
  number 
  of 
  nymphs 
  were 
  obtained, 
  both 
  from 
  Little 
  

   dear 
  creek 
  beside 
  the 
  hatchery 
  and 
  from 
  the 
  hatchery 
  trou^s. 
  

  

  Caenis 
  diminuta 
  Walker 
  

  

  1853 
  Caenis 
  diminuta 
  Walker, 
  List 
  neur. 
  ins. 
  Brit. 
  nms. 
  3 
  : 
  584 
  

  

  1861 
  Caenis 
  diminuta 
  Ha 
  gen 
  , 
  Synopsis 
  Neur. 
  N. 
  Am. 
  p. 
  55 
  

  

  1861 
  Caenis 
  arnica 
  Hageu, 
  Synopsis 
  Neur. 
  N.~-Am. 
  p. 
  55 
  

  

  1871 
  Caenis 
  diminuta 
  Eaton, 
  Ent. 
  soc. 
  Lond. 
  Trans, 
  p. 
  95 
  (description 
  

  

  in 
  Latin) 
  

   1885 
  Caenis 
  diminuta 
  Eaton, 
  Linn. 
  soc. 
  Lond. 
  Trans. 
  (2) 
  3 
  : 
  147 
  (a 
  full 
  

  

  description) 
  

   1892 
  Caenis 
  diminuta 
  Banks, 
  Am. 
  ent. 
  soc. 
  Trans. 
  19 
  : 
  348 
  (listed) 
  

  

  This 
  dumpy, 
  little, 
  nocturnal 
  species 
  was 
  taken 
  abundantly 
  in 
  a 
  trap 
  

   lantern 
  hung 
  on 
  the 
  side 
  of 
  the 
  boathouse 
  at 
  the 
  outlet 
  of 
  Little 
  Clear 
  

   pond. 
  15 
  to 
  50 
  specimens 
  were 
  taken 
  at 
  a 
  single 
  lantern 
  each 
  evening 
  

   from 
  the 
  14th 
  to 
  the 
  j8th 
  of 
  July. 
  This 
  appeared 
  to 
  be 
  the 
  season 
  

   of 
  greatest 
  abundance 
  for 
  the 
  species. 
  It 
  is 
  quite 
  variable 
  in 
  size 
  

   and 
  in 
  coloration 
  : 
  the 
  best 
  colored 
  of 
  my 
  specimens 
  agree 
  well 
  with 
  

   Eaton's 
  detailed 
  description 
  ; 
  but 
  the 
  size 
  is 
  often 
  much 
  larger, 
  reaching 
  

   5-6 
  mm 
  in 
  length. 
  This 
  may 
  be 
  due 
  to 
  the 
  taking 
  of 
  published 
  measure- 
  

   ments 
  from 
  dried 
  specimens, 
  which 
  are 
  always 
  shriveled 
  considerably. 
  

   The 
  species 
  is 
  generally 
  distributed 
  over 
  the 
  eastern 
  United 
  States. 
  

  

  The 
  nymphs 
  are 
  common 
  among 
  the 
  trash 
  on 
  the 
  bottom 
  in 
  all 
  quiet 
  

   waters. 
  Their 
  inconspicuous 
  coloration 
  and 
  trashy 
  covering 
  protect 
  

  

  