﻿496 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Helocordulia 
  is 
  most 
  nearly 
  allied 
  to 
  Tetragoneuria. 
  

   There 
  are 
  however 
  a 
  few 
  venational 
  characters 
  which 
  readily 
  distinguish 
  

   the 
  two 
  genera. 
  

  

  CHABACTEE 
  

  

  TETRAGONEURIA 
  

  

  HELOCORDULIA 
  

  

  2d 
  cubito-anal 
  cross 
  vein 
  

  

  absent 
  

  

  nearly 
  always 
  present 
  

  

  Uuder 
  the 
  stigma 
  

  

  a 
  single 
  cross 
  vein 
  fol- 
  

   lowed 
  by 
  a 
  wide 
  space 
  

  

  two 
  cross 
  veins 
  and 
  more 
  

   normal 
  spaces 
  

  

  Autenodal 
  cross 
  veins 
  of 
  

   the 
  hind 
  wing 
  

  

  four 
  or 
  five 
  

  

  six 
  

  

  The 
  anal 
  loop 
  is 
  slightly 
  wider 
  and 
  more 
  oblique 
  at 
  the 
  apex 
  in 
  Tetra- 
  

   goneuria. 
  T.spinosa 
  has 
  the 
  antenodal 
  cross 
  veins 
  spotted 
  with 
  

   fuscous 
  much 
  as 
  in 
  Helocordulia. 
  

  

  The 
  nymph 
  of 
  Helocordulia 
  is 
  pecuHar 
  among 
  the 
  known 
  cor- 
  

   duline 
  nymphs 
  in 
  having 
  dorsal 
  hooks 
  on 
  segments 
  6-9 
  only, 
  with 
  some 
  

  

  Fig. 
  21 
  Helocordulia, 
  genitalia: 
  a;, 
  y 
  ( 
  ^ 
  ) 
  and 
  2; 
  ( 
  $ 
  ) 
  of 
  H. 
  uhleri 
  Selys: 
  a, 
  b 
  (ventral 
  

   view), 
  c 
  ( 
  5 
  ) 
  and 
  d 
  ( 
  $ 
  ) 
  of 
  H. 
  selysi 
  Hag. 
  

  

  of 
  these 
  distinctly 
  cultriform, 
  and 
  in 
  the 
  extreme 
  abbreviation 
  of 
  the 
  

   ninth 
  abdominal 
  segment 
  on 
  the 
  dorsal 
  side, 
  so 
  that 
  its 
  dorsal 
  length 
  is 
  

   less 
  than 
  half 
  its 
  ventral. 
  

  

  The 
  two 
  species 
  of 
  the 
  genus 
  may 
  be 
  separated 
  as 
  imagos 
  by 
  reference 
  

   to 
  the 
  figures 
  herewith 
  presented. 
  The 
  nymph 
  is 
  known 
  for 
  but 
  one 
  of 
  

   these, 
  H. 
  uhleri, 
  the 
  only 
  one 
  apparently 
  belonging 
  to 
  the 
  New 
  

   York 
  fauna. 
  

  

  