492 U. S. NATIONAL MUSEUM BULLETIN 216 



Key to the Nearctic subgenera, species groups, and species of Xorides 



1. Median lobe of mesoscutum with a broad median longitudinal groove; second 



trochanter of front leg -with a subapical thorn in front; temple with strong, 

 mostly longitudinal striae (fig. 315,g); tooth at upper end of epomia 

 exceptionally strong and projecting. Subgenus Exomus. 



1. humeralis (Say) 



Median lobe of mesoscutum without a median longitudinal groove; second 



trochanter of front leg without a thorn; temple often with striae, but when 



present these are usually oblique. Subgenus Xorides 2 



2. Temple conspicuously marked with white, its lower half obliquely striate. 



Albopictus group (p. 515) 3 



Temple not marked with white except in X. pictus, in which the temple is not 

 striate 4 



3. Basal four abdominal tergites entirely blackish in male, entirely ferruginous 



in female; occipital carina complete 13. calidus (Provancher) 



Basal four abdominal tergites black with prominent white marks; occipital 

 carina narrowly interrupted medially above . . 14. albopictus (Cresson) 



4. Occipital carina incomplete above, broadly interrupted medially .... 5 

 Occipital carina complete 11 



5. First abdominal segment relatively stout, its basal third strongly arched 



above, the rest almost straight; striae on upper half of temple, when distinct, 



subhorizontal (fig. 316,g). Maudae group (p. 520) 6 



First abdominal segment slender, its basal third moderately arched, the rest 

 weakly arched or almost straight; striae on upper half of temple, when 

 present, subvertical (fig. 316, h). Stigmapterus group (p. 522) . ... 8 



6. Temple not swollen beyond outside tangent of eye, its upper third without 



distinct striae; basitarsi of middle and hind legs white basally, the rest 



brown or black 15. atrox, new species 



Temple swollen a little beyond outside tangent of eye, its upper third with 

 longitudinal striae; basitarsi uniformly dark brown 7 



7. Scutellum laterally and pronotum at upper end of notaulus, ivory ; flagellum 



of female entirely blackish; top of head without transverse rugulae. 



16. maudae (Davis) 

 Scutellum and pronotum without ivory marks; flagellum of female with a 

 narrow white band; top of head with weak transverse rugulae. 



17. neoclyti (Rohwer) 



8. Tibiae and basitarsi white basally, the rest black or the front basitarsus some- 



times entirely white; body always black 9 



Tibiae and basitarsi uniformly fulvous to black, not white at base; body 

 black to fulvous 10 



9. First tergite rather broad, its sternite surpassing spiracle by about 0.5 the 



average width of the sternite in male, ending at the spiracle in female; first 

 and second segments of front tarsus entirely white; median longitudinal 

 carinae of first tergite obsolete apicad of the spiracle; upper face of front 

 tibia of male entirely white; segments of female flagellum at the subapical 

 bend about 0.8 as long as wide (fig. 329,a) . . 18. harringtoni (Rohwer) 

 First tergite narrow, its sternite surpassing spiracle by about 1.3 the average 

 width of the sternite in male, by about 0.5 the average width of sternite in 

 female; first and second segments of front tarsus black or infuscate, the 

 base of first segment white; median longitudinal carinae extending beyond 

 spiracle as distinct ridges; upper face of front tibia of male blackish, its 

 base white; segments of female flagellum at subapical bend about 1.1 as 

 long as wide (fig. 329,b) 20. stigmapterus (Say) 



