396 U. S. NATIONAL MUSEUM BULLETIN 216 



1. Genus Rhyssa 



Figure 302,b 



Rhyssa Gravenhorst, 1829, Ichneumologia europaea, vol. 3, p. 260. Type: 

 Ichneumon persuasorhis Linnaeus; designated by Westwood, 1839. 



Cryptocentrum Kirby, 1837, in Richardson, Fauna boreali americana, pt. 4, p. 260. 

 Type: Cryptocentrum lineolatum Kirby; monobasic. 



Pararhyssa Walsh, 1873, Trans. Acad. Sci. St. Louis, vol. 3, p. 109. Type: 

 Ichneumon persuasorhis Linnaeus; designated by Viereck, 1914. 



Front wing 6 to 24 mm. long; clypeus with a median apical tubercle 

 but without lateral apical tubercles; junction of occipital and hypo- 

 stomal carinae distant from base of mandible by about 0.4 the basal 

 width of mandible; mandibular teeth of equal length, the lower tooth 

 pointed at apex, the upper tooth chisel-shaped; second trochanter of 

 middle leg without a ventral longitudinal ridge; stigma about 6.5 as 

 long as wide; areolet present, sometimes absent in small males; first 

 tergite free from its sternite, with a distinct glymma; tergites 3 to 

 6 of male cylindric or weakly compressed, with a transverse mat sculp- 

 ture, with moderately dense hairs, their apical margins very weakly 

 concave medially; tergites 3 to 6 of female with a transverse mat or 

 finely aciculate sculpture, with sparse short hairs; sternites 3 to 6 

 of female with a pair of tubercles near their midlength; apical tergite 

 of female with a median apical horny point whose apex is truncate; 

 male clasper short, evenly convex and rather densely hairy, its apex 

 broadly rounded and with a broad shallow notch. 



This genus is Holarctic. All species seem to be parasitic on borers 

 in conifers, particularly in the northern conifers. They are common 

 in our Canadian zone. Except for R. hoferi, which has a reddish 

 brown color, the species are mostly black with numerous large white 

 spots. Certain details in the white spotting are useful for distinguish- 

 ing species. 



Key to the Nearctic species of Rhyssa 



1. First four tergites with a narrow whitish apical margin, the margin of even 



width and continuous across the middle or a little narrower and sometimes 

 a little interrupted medially (figs. 317,a,b); third tergite of both sexes with 

 short hairs that are moderately dense and evenly distributed. Hoferi 



group 2 



First four tergites with white apical spots that do not form a continuous band 

 from one side to the other (figs. 317,c-g); second and third tergites with 

 short hairs that are sparse to moderately dense in male, sparse and usually 

 irregularly distributed in female 3 



2. Body ground color black; fore wing hyaline, not marked. 



1. howdenorum, new species 

 Body ground color rufous; fore wing marked with rufous brown (fig. 319,a). 



2. hoferi Rohwer 



