﻿AQUATIC 
  INSECTS 
  IN 
  THE 
  ADIRONDACKS 
  445 
  

  

  12 
  Two 
  cells 
  between 
  veins 
  Ai 
  and 
  As 
  at 
  their 
  origin 
  ; 
  length 
  less 
  than 
  

  

  45 
  mm 
  brevis 
  

  

  A 
  single 
  cell 
  between 
  veins 
  Ai 
  and 
  A2 
  at 
  their 
  origin 
  ; 
  length 
  more 
  than 
  

   45 
  mm 
  13 
  

  

  13 
  Midlateral 
  thoracic 
  stripe 
  complete 
  : 
  length 
  about 
  46 
  mm 
  adelphus 
  

  

  Midlateral 
  thoracic 
  stripe 
  interrupted, 
  not 
  exteudiug 
  above 
  the 
  spiracle 
  : 
  

  

  length 
  about 
  54 
  mm 
  vastus 
  

  

  14 
  Ninth 
  abdominal 
  segment 
  little 
  longer 
  than 
  the 
  eighth, 
  ground 
  color 
  

  

  brown 
  plagiatus 
  

  

  Ninth 
  abdominal 
  segment 
  much 
  longer 
  than 
  the 
  eighth; 
  ground 
  color 
  

   black 
  spiniceps 
  

  

  SYNOPTIC 
  ARRANGEMENT 
  OF 
  THE 
  GENUS, 
  IMAGOS 
  AND 
  NYMPHS 
  

  

  Subgenus 
  gomphus 
  

  

  Imago. 
  Generally 
  with 
  two 
  cells 
  between 
  veins 
  Ai 
  and 
  A2 
  at 
  their 
  

   origin, 
  when 
  with 
  but 
  one, 
  that 
  one 
  generally 
  longer 
  (in 
  the 
  axis 
  of 
  the 
  

   wing) 
  than 
  wide, 
  and 
  never 
  so 
  thickened 
  in 
  its 
  bordering 
  veins 
  as 
  to 
  con- 
  

   stitute 
  a 
  distinct 
  anal 
  loop; 
  hind 
  femora 
  similar 
  in 
  the 
  two 
  sexes; 
  pos- 
  

   terior 
  genital 
  hamule 
  in 
  the 
  male 
  generally 
  nearly 
  vertical 
  in 
  direction, 
  

   at 
  least 
  not 
  directed 
  anteriorly; 
  eighth 
  abdominal 
  segment 
  generally 
  

   squarely 
  cut, 
  rarely 
  a 
  very 
  little 
  longer 
  on 
  the 
  dorsal 
  than 
  on 
  the 
  ventral 
  

   side. 
  

  

  Nymph. 
  Abdomen 
  wider 
  than 
  the 
  head; 
  lateral 
  spines 
  on 
  abdominal 
  

   segments 
  6-9 
  ; 
  an 
  impressed 
  middorsal 
  hne 
  on 
  abdomen 
  more 
  or 
  less 
  

   >€vident, 
  often 
  appearing 
  to 
  divide 
  the 
  segments 
  longitudinally, 
  present 
  

   even 
  on 
  the 
  bases 
  of 
  segments 
  which 
  may 
  bear 
  dorsal 
  hooks 
  apically 
  ; 
  

   median 
  lobe 
  of 
  labium 
  straight 
  on 
  anterior 
  border, 
  or 
  very 
  slightly 
  con- 
  

   vex, 
  and 
  not 
  bearing 
  a 
  median 
  tooth. 
  

  

  A 
  synthetic 
  group, 
  offering 
  evident 
  points 
  of 
  departure 
  for 
  the 
  three 
  

   subgenera 
  which 
  follow 
  it. 
  

  

  KEY 
  

  

  1) 
  Ninth 
  abdominal 
  segment 
  a 
  little 
  shorter 
  than 
  the 
  eighth 
  ; 
  two 
  cells 
  be- 
  

  

  tween 
  veins 
  Ai 
  and 
  A2 
  at 
  their 
  origin; 
  male 
  with 
  the 
  fork 
  of 
  the 
  in- 
  

   ferior 
  abdominal 
  appendage 
  not 
  extending 
  laterally 
  beyond 
  the 
  superiors; 
  

   female 
  with 
  a 
  low 
  carina 
  on 
  the 
  vertex, 
  at 
  whose 
  extremities 
  arise 
  black 
  

   thornlike 
  spines; 
  small 
  species. 
  

  

  a) 
  Imago 
  Face 
  yellow 
  : 
  Nymph 
  Length 
  when 
  full 
  grown 
  24 
  mm 
  ; 
  

   lateral 
  spine 
  on 
  the 
  sixth 
  abdominal 
  segment 
  less 
  than 
  half 
  the 
  length 
  

   of 
  the 
  one 
  on 
  the 
  seventh 
  segment 
  G. 
  abbreviatus 
  

  

  aa) 
  Imago 
  Face 
  transversely 
  lineate 
  with 
  black. 
  JVym^^/i 
  Length 
  when 
  

   full 
  grown 
  26 
  mm 
  ; 
  lateral 
  spine 
  on 
  the 
  sixth 
  abominal 
  segment 
  more 
  than 
  

   half 
  as 
  long 
  as 
  the 
  one 
  on 
  the 
  seventh 
  segment 
  G. 
  brevis 
  

  

  2) 
  Ninth 
  abdominal 
  segment 
  as 
  long 
  as 
  the 
  eighth, 
  or 
  often 
  a 
  very 
  little 
  

  

  longer; 
  inferior 
  abdominal 
  appendage 
  of 
  the 
  male 
  widely 
  forked, 
  its 
  

  

  