16 U. S. NATIONAL MUSEUM BULLETIN 216 



first tergite ascending from base of tergite at an angle of 20° to 65°; 

 second tergite without an oblique groove on either side at base; hind 

 margin of subgenital plate of male truncate or biemarginate and with 

 edge not upturned; ninth tergite (concealed in dried specimens) of 

 male without a distinct process (appendiculum) at base; subgenital 

 plate of female with a small to very large membranous excision at 

 base ; sheath rather densely clothed with rather long, suberect, basally 

 compressed hairs; ovipositor weakly to strongly compressed, the upper 

 valve usually with a preapical crest or "nodus," the lower valve usually 

 with several, distinct, oblique or transverse ridges before apex. 



In most members of the genus the body is black and the legs are 

 mostly reddish to yellowish, the hind tibia whitish with distinct sub- 

 basal and apical fuscous annuli. Less frequently the thorax and 

 abdomen are more or less red and the hind tibia may lack distinct 

 markings. 



Scambus seems most closely related to Exeristes, its resemblance 

 being especially evident in such species as E. comstockii (Cresson). 

 It appears less closely allied to Acropimpia, Iseropus, Tromatobia, and 

 Alophosternum, but because of certain similarities it has often been 

 confused with them in collections. 



As here recognized the genus is rather broadly denned. It is divided 

 into five subgenera. Three of these, Ateleophadnus, Endromopoda 

 and Scambus, are Holarctic, and they include the majority of the 

 members of the genus. The other two, Lissoscambus and Erythro- 

 scambus, are known only from a few North American species, the 

 former from the Sonoran faunal area of the Nearctic and the latter 

 largely from the Neotropic region. 



The subgenera are distinguished principally by the differences given 

 in the keys below. In using the keys, wherever possible it is desirable 

 to have both sexes represented. Special care is required in distinguish- 

 ing between the males of Endromopoda and Scarnbus. 



Keys to the subgenera of Scambus 



MALES 



1. Submetapleural carina usually absent; mesoscutum mostly bare or with only 

 very sparse hairs, occasionally with moderately dense hairs; propodeum 

 without distinct dorsomedial carinae, sometimes with a shallow, median, 

 longitudinal sulcus; first tergite with dorsal carinae absent or indistinct 

 beyond apex of basal declivity; thorax red, with a few conspicuous black 

 markings; front and middle legs, and hind tibia and tarsus, mostly whitish 

 or creamy-white, the hind tibia sometimes with a few fuscous streaks or 



spots but without distinct fuscous annuli 2 



Submetapleural carina present; mesoscutum with rather evenly distributed, 

 moderately dense hairs; propodeum usually with distinct (sometimes rather 

 short) dorsomedial carinae; first tergite with dorsal carinae usually distinct 



