164 ILLINOIS ACADEMY OF SCIENCE 



— . Second and third dorsal abdominal segments not both 



ferruginous 12 



11. Ocelli just below the supra-orbital line ; occiput usually domi- 



nantly yellow ; black band between the bases of the wings 

 more or less indistinct ; fourth dorsal abdominal segment 



with ferruginous pubescence rufocinctus Cress. 



— . Ocelli not placed l)elow the supra-orbital line ; occiput usually 

 domiuantly black ; black band between the bases of the 

 wings distinct and broad, with its posterior margin extending 

 backward in the form of a Y ; fourth dorsal abdominal seg- 

 ment with yellow pubescence ternarius Say. 



12. Last two dorsal abdominal segments with black pubescence 



dominant; orbicular fringes black rufocinctus Cress. 



• — . Last two dorsal abdominal segments with light ferruginous 

 pubescence dominant, corbicular fringes with some ferru- 

 ginous hairs frigidus F. Sm. 



13. Second dorsal abdominal segment entirely black impatiens Cress. 



- — . Second dorsal abdominal segment not entirely black 14 



14. First dorsal abdominal segment yellow ; second segment, ex- 



cept for a basal medial tawny patch, black ; remaining 

 segments black ; ocelli placed well below the supra-orbital 



line separatus Cress. 



— . Dorsal alidominal segments not so colored ; in some species the 



ocelli not below the supra-orbital line 15 



15. First four dorsal abdominal segments yellow ; fifth and sixth 



segments ))lack fcrvidus subsp. dorsalis Cress. 



- — . Dorsal abdominal segments not so colored IG 



16. Yellow pubescence of the pleura not extending to the bases of 



the legs 17 



— . Yellow pul)escence of the pleura, at least the mesopleura, ex- 

 tending to the liases of the legs 19 



17. Malar space longer than its width at lower margin ; ocelli 



placed well below the supra-orbital line ; first three dorsal 

 abdominal segments mostly yellow ; the remaining segments 

 black nevadensis Cress. 



— . Malar space not longer than its width at lower margin ; ocelli 

 not placed below the supra-orbital line or only slightly so ; 

 first three dorsal abdominal segments not as above 18 



IS. Ocelli placed near the supra-orbital line, above the narrowest 

 part of the vertex ; malar space about as long as its width at 

 lower margin ; first two dorsal abdominal segments usually 

 yellow, and the remaining segments black perplexus Cress. 



— . Ocelli placed just above the supra-orbital line ; malar space 

 shorter than its width at lower margin ; second and third 

 dorsal abdominal segments usually with some ferrguinous 

 pubescence, but the second segment sometimes with a basal • 

 middle patch of yellow pubescence, the remainder of the 

 segment being black rufocinctus Cress. 



19. First dorsal abdominal segment and a medial basal patch of the 



second segment yellow ; remaining segments black 



bimaculatus Cress. 



— . Dorsal abdominal segments not so colored 20 



20. First two dorsal abdominal segments yellow vagans F. Sm. 



— First dorsal abdominal segment yellow, second segment with 



ferruginous and yellow pubescence affinis Cress. 



Key for the Separation of the Males of the Genus 



Psithyrus from Illinois. 



1. Yellow pubescence of the thorax extending down on the pleura 



to the bases of the legs 2 



