ICHNEUMON-FLIES — GELINAE : MESOSTENINI 469 



enclosing tip of dorsal valve, their teeth in the form of strong vertical 

 ridges. 



Acroricnus is a small genus that is widel}^ distributed in the North- 

 ern Hemisphere. Only one species occm's in the United States. It 

 was studied in some detail by Mitchell, who has divided it into a 

 number of subspecies. The treatment below is taken from his publi- 

 cation (1950, Ann. Ent. Soc. America, vol. 43, pp. 251-260). Dis- 

 tributional data are cited only from specimens seen by ourselves, but 

 the distributional maps are made to include also the localities pub- 

 hshed by Mitchell. 



1. Acroricnus sty la tor (Thunberg) 



Front wing 6.5 to 11.5 mm. long; prepectal carina complete, 

 extending upward and forward to near front margin of mesopleurum; 

 transverse carinae of propodeum rather distinct; groove between pro- 

 podeum and metapleurum deep and strongly foveolate; hind spur of 

 hind tibia more than half as long as its basitarsus. 



Coloration variable, according to the subspecies. Wings subhyaline 

 or in the subspecies edwardsii with a yellow tinge. 



This is a Holarctic species, with a number of subspecies. Adidts 

 occur through summer and early fall. The usual habitat is rather 

 open, partly forested country and overgrown fields. Specimens are 

 frequently seen on windows of buildings, presumably because many of 

 their hosts nest around buildings and the species characteristically 

 explores such situations. They are also rather common on umbel- 

 liferous flowers. It has been reared repeatedly from the mud nests of 

 Ancistrocerus, Eumenes, and Sceliphron. In the case of the rearings 

 from Sceliphron nests, it is not certain whether the host was Sceliphron 

 itself or a eumenine vespid that made its nests in abandoned nests of 

 Sceliphron. 



The Nearctic subspecies are keyed and described below: 



1. Abdomen prominently marked with yellow; range: central California to 



southern Oregon Ih. stylator edwardsii (Cresson) 



Abdomen not prominently marked with yellow 2 



2. Hind tibia entirely yellow 3 



Hind tibia yellow with its apical 0.3 ± fuscous 5 



3. Propodeum, metapleurum, and hind coxa entirely black; scutellum black or 



yellow; range: Canadian zone and adjacent part of Transition zone east of 



Rocky Mountains If. stylator aequatus (Say) 



Propodeum, metapleurum, and hind coxa, or at least one of them, marked with 

 yellow; scutellum entirely yellow 4 



4. Hind femur broadly fulvous basally; range: New Mexico and Arizona. 



Id. stylator townesi Mitchell 



Hind femur entirely black or only its extreme base fulvous; range: Alleghanian 



and Carolinian faunas le. stylator junceus (Cresson) 



