﻿AQUATIC 
  INSECTS 
  IN 
  THE 
  ADIRONDACKS 
  485 
  

  

  t 
  

   dd 
  Wings 
  clear 
  ; 
  inferior 
  abdominal 
  appendage 
  of 
  the 
  male 
  deeply 
  bifur- 
  

   cated, 
  the 
  forks 
  again 
  notched 
  at 
  tips 
  ; 
  never 
  with 
  less 
  than 
  five 
  

   antenodals 
  in 
  the 
  hind 
  vring, 
  or 
  v^ith 
  the 
  triangle 
  of 
  that 
  wing 
  

  

  traversed 
  by 
  a 
  cross 
  vein 
  Cordulia 
  

  

  cc 
  Triangles 
  of 
  the 
  fore 
  wiugs 
  open 
  Doroeordulia 
  

  

  So 
  well 
  marked 
  are 
  these 
  genera 
  that 
  they 
  may 
  generally 
  be 
  recognized 
  

  

  at 
  a 
  glance 
  by 
  the 
  following. 
  

  

  Single 
  distinctive 
  characters 
  

   Epicordulia 
  alone 
  has 
  large 
  brown 
  spots 
  at 
  base, 
  nodus 
  and 
  stigma 
  

  

  of 
  all 
  wings. 
  

   Tetragoneuria 
  alone 
  has 
  but 
  four 
  antenodals 
  in 
  the 
  hind 
  wing. 
  

   Helocordulia 
  alone 
  has 
  the 
  stigma 
  very 
  narrowly 
  diamond-shaped, 
  

  

  with 
  the 
  ends 
  of 
  it 
  meeting 
  the 
  sides 
  by 
  an 
  angle 
  of 
  3o°-35°. 
  

   Cordulia 
  alone 
  has 
  the 
  inferior 
  abdominal 
  appendage 
  of 
  the 
  male 
  

  

  deeply 
  bifurcated. 
  

   Doroeordulia 
  alone 
  has 
  the 
  triangle 
  of 
  the 
  fore 
  wing 
  free 
  from 
  cross 
  

  

  veins. 
  

   Neurocordulia 
  has 
  been 
  sufficiently 
  distinguished 
  above 
  ; 
  S 
  o 
  m 
  a 
  t 
  - 
  

  

  o 
  c 
  h 
  1 
  o 
  r 
  a 
  possesses 
  none 
  of 
  the 
  characters 
  of 
  this 
  list. 
  

  

  Nymphs 
  

  

  a 
  Lateral 
  setae 
  four 
  or 
  five 
  ; 
  mentum 
  about 
  as 
  loug 
  as 
  wide.. 
  Epicordulia 
  

   aa 
  Lateral 
  setae 
  seven 
  ; 
  mentum 
  of 
  labium 
  longer 
  than 
  wide 
  

  

  & 
  Abdomen 
  with 
  large, 
  laterally 
  flattened, 
  generally 
  cultriform 
  dorsal 
  hooks 
  

  

  c 
  Lateral 
  spines 
  of 
  the 
  ninth 
  segment 
  longer 
  than 
  half 
  the 
  length 
  of 
  that 
  

  

  segment 
  ; 
  dorsal 
  hooks 
  on 
  segments 
  3-9, 
  highest 
  on 
  6, 
  cultriform, 
  and 
  

  

  sharp 
  Tetragoneuria 
  

  

  cc 
  Lateral 
  spines 
  of 
  the 
  ninth 
  segment 
  shorter 
  than 
  half 
  of 
  that 
  segment 
  ; 
  

   dorsal 
  hooks 
  less 
  developed 
  

   d 
  Dorsal 
  hooks 
  on 
  segments 
  4-9 
  laterally 
  flattened, 
  but 
  obtuse 
  at 
  apices, 
  

  

  and 
  not 
  cultriform 
  Somatochlora^ 
  

  

  dd 
  Dorsal 
  hooks 
  on 
  segments 
  6-9, 
  longest 
  on 
  8 
  and 
  cultriform 
  

  

  He 
  loeordulia 
  

   6& 
  Abdomen 
  with 
  no 
  dorsal 
  hooks, 
  or 
  with 
  these 
  rudimentary, 
  not 
  flattened 
  

   laterally 
  or 
  cultriform, 
  but 
  small 
  obtuse 
  or 
  pointed 
  prominences 
  

   c 
  Hind 
  angles 
  of 
  the 
  head 
  rounded 
  ; 
  lateral 
  spines 
  of 
  the 
  ninth 
  abdominal 
  

  

  segment 
  one 
  fifth 
  as 
  long 
  as 
  that 
  segment 
  Cordulia 
  

  

  cc 
  Hind 
  angles 
  of 
  the 
  head 
  angulate 
  superiorly 
  ; 
  spines 
  of 
  the 
  ninth 
  abdom- 
  

   inal 
  segment 
  one 
  third 
  as 
  long 
  as 
  that 
  segment 
  Doroeordulia 
  

  

  1 
  There 
  can 
  be 
  little 
  doubt 
  that 
  the 
  unknown 
  nymphs 
  of 
  the 
  numerous 
  species 
  of 
  this 
  genus 
  will 
  

   necessitate 
  an 
  amplification 
  of 
  the 
  characters 
  herein 
  stated. 
  S. 
  elongata 
  appears 
  to 
  be 
  the 
  only 
  

   American 
  species 
  yet 
  reared. 
  Cabot 
  described 
  a 
  nymph 
  as 
  that 
  ofSom. 
  albicincta, 
  supposition, 
  

   but 
  I 
  am 
  unable 
  to 
  say 
  whether 
  the 
  supposition 
  was 
  correct 
  : 
  so 
  far 
  as 
  one 
  may 
  judge 
  from 
  his 
  figure, 
  

   that 
  one 
  might 
  as 
  well 
  have 
  been 
  Cordulia 
  shurtleffl. 
  The 
  typical 
  Somatochlora 
  

   metallica 
  of 
  Europe 
  has 
  dorsal 
  hooks 
  on 
  segments 
  3-9 
  of 
  abdomen, 
  with 
  the 
  posterior 
  ones 
  bet- 
  

   ter 
  developed 
  than 
  in 
  S. 
  e 
  1 
  o 
  n 
  g 
  a 
  t 
  a 
  . 
  It 
  must 
  be 
  borne 
  in 
  mind 
  by 
  those 
  who 
  use 
  this 
  table 
  that 
  it 
  

   Is 
  based 
  only 
  on 
  the 
  nymphs 
  of 
  the 
  species 
  herein 
  described. 
  

  

  