﻿65 
  

  

  4 
  (5) 
  First 
  and 
  second 
  abdominal 
  segments 
  for 
  the 
  most 
  part 
  red, 
  

  

  second 
  sometimes 
  black 
  or 
  fuscous 
  at 
  base 
  and 
  apex 
  but 
  

   red 
  on 
  the 
  disc. 
  O. 
  frater, 
  D. 
  T. 
  

  

  5 
  (4) 
  First 
  and 
  second 
  abdominal 
  segments 
  not 
  for 
  the 
  most 
  part 
  

  

  red, 
  if 
  the 
  first 
  is 
  red 
  then 
  the 
  second 
  is 
  always 
  black 
  on 
  

   the 
  disc. 
  

  

  6 
  (7) 
  Second 
  ventral 
  segment 
  extremely 
  strongly 
  and 
  abruptly 
  

  

  raised 
  behind 
  the 
  transverse 
  sulcature 
  to 
  a 
  height 
  much 
  

   greater 
  than 
  that 
  of 
  the 
  basal 
  part 
  of 
  the 
  segment, 
  the 
  

   sulcature 
  smooth 
  and 
  without 
  costae. 
  O. 
  hontoeogaster, 
  P. 
  

  

  7 
  (6) 
  Second 
  ventral 
  segment 
  not 
  very 
  greatly 
  raised, 
  if 
  moderately 
  

  

  raised 
  then 
  the 
  costae 
  are 
  present 
  and 
  the 
  sulcature 
  is 
  not 
  

   smooth 
  and 
  shining. 
  

  

  8 
  (13) 
  Clj^peus 
  of 
  the 
  male 
  extremely 
  strongly 
  emarginate, 
  the 
  emar- 
  

  

  gination 
  hardly 
  less 
  than 
  semi-circular 
  or 
  even 
  stronger; 
  

   female 
  with 
  the 
  clypeus 
  strongly 
  and 
  distinctly 
  emarginate, 
  

   but 
  sometimes 
  much 
  less 
  deeply 
  than 
  that 
  of 
  the 
  male. 
  

  

  9 
  (12) 
  Basal 
  abdominal 
  segment 
  for 
  the 
  most 
  part 
  red; 
  second 
  ventral 
  

  

  segment 
  with 
  a 
  shallow, 
  or 
  very 
  shallow 
  and 
  vague, 
  depres- 
  

   sion 
  beyond 
  the 
  costae. 
  

  

  10 
  (11) 
  Smaller, 
  length 
  to 
  apex 
  of 
  second 
  abdominal 
  segment 
  less 
  than 
  

  

  nine 
  mm. 
  ; 
  no 
  median 
  yellow 
  frontal 
  spot 
  ; 
  punctures 
  of 
  

   basal 
  abdominal 
  segment 
  effaced 
  over 
  almost 
  the 
  whole 
  

   surface. 
  O. 
  monas, 
  sp. 
  nov. 
  

  

  11 
  (10) 
  Larger, 
  length 
  to 
  apex 
  of 
  second 
  segment 
  not 
  less 
  than 
  nine 
  

  

  mm. 
  head 
  with 
  a 
  median 
  yellow 
  spot 
  ; 
  puncturation 
  of 
  basal 
  

   abdominal 
  segment 
  shallow, 
  but 
  conspicuous. 
  

  

  O. 
  cepJialostictus, 
  P. 
  

  

  12 
  (9) 
  Basal 
  abdominal 
  segment 
  with 
  a 
  red 
  apical 
  band 
  dilated 
  at 
  the 
  

  

  sides; 
  second 
  ventral 
  segment 
  with 
  a 
  deep 
  and 
  distinct 
  

   depression. 
  O. 
  naiadum, 
  P. 
  

  

  13 
  (8) 
  Male 
  clypeus 
  not 
  extremel}^ 
  deeply 
  emarginate; 
  in 
  the 
  female 
  

  

  the 
  true 
  emargination 
  slight, 
  or 
  the 
  apex 
  is 
  truncate. 
  

  

  14 
  (15) 
  Clypeus 
  distinctly 
  red-marked 
  on 
  the 
  basal 
  half; 
  (pronotum 
  

  

  and 
  apical 
  margin 
  of 
  first 
  abdominal 
  segment 
  always 
  red- 
  

   marked, 
  second 
  segment 
  entirely 
  black 
  and 
  the 
  mandibles 
  

   mostly 
  dark. 
  O. 
  tempe, 
  sp. 
  nov. 
  

  

  15 
  (14) 
  Clypeus 
  not 
  marked 
  with 
  red 
  on 
  the 
  basal 
  part; 
  (pronotum 
  in 
  

  

  some 
  species 
  entirely 
  black, 
  second 
  segment 
  in 
  many 
  species 
  

   red-marked, 
  mandibles 
  sometimes 
  red). 
  

  

  16 
  (27) 
  Prothorax 
  with 
  red-markings. 
  

  

  17 
  (22) 
  Propodeum 
  always 
  red 
  or 
  red-marked. 
  

  

  18 
  (21) 
  Apical 
  margin 
  of 
  the 
  second 
  abdominal 
  segment 
  red. 
  

  

  19 
  (20) 
  Basal 
  abdominal 
  segment 
  with 
  an 
  apical 
  red 
  band 
  strongly 
  

  

  dilated 
  at 
  the 
  sides; 
  mesothorax 
  somewhat 
  finely 
  and 
  

   irregularly 
  punctured. 
  O. 
  dryas, 
  P. 
  

  

  20 
  (19) 
  Basal 
  segment 
  nearly 
  entirely 
  red; 
  mesothoracic 
  punctures 
  

  

  coarse. 
  O. 
  potantophilus, 
  P. 
  

  

  