116 BULLETIN 66, UNITED STATES NATIONAL MUSEUM. 



Homilopinse Pierce, parasitic on Sphecoidea. 

 Halictoxeninae Pierce, parasitic on Apoidea. 

 Crawfordinse Pierce, parasitic on Apoidea. 



1. Subfamily XENIN^C Pierce, 1908. 



Type genus. — Xenos Rossi (1794). 



Parasitic on Vespoidea and possibly Sphecoidea. 



Maxillae two-jointed. 



The subfamily is composed of four tribes: 



Xenini Pierce, parasitic on Vespidse; Europe, America, Asia. 



Pseudoxenini Pierce, parasitic on Rumenidae; Europe, America. 



Paraxenini Pierce, parasitic on Bembecidse; Europe. 



phihalmochlini Pierce, parasitic on Sphecidse; America. 



1. XENINI, new tribe. 



Xenides Saunders, 1872. 



Xenini Perkins, 1906, in correspondence. 



Type-genus. — Xenos Rossi (1790). 



Parasites of Vespidse. 



The tribe includes four genera: 



9. Xenos Rossi (1790), parasitic on Polistes; Europe. 



10. Acroschismus Pierce (1908), parasitic on Polistes; America. 



11. ScMstosiphon Pierce (1908), parasitic on Polistes; America. 



12. Vespaexenos Pierce, parasitic on Vespa; Asia. 



9. Genus XENOS Rossi (1790), redefined. 



Ichneumon Rossi, 1793. , 



Xenos Kirby, 1813.— Hoeven, 1850.— Saunders, 1872.— Pierce, 1908. 



Xenus Rye, 1875. — Century Dictionary, 1897: — Stiles, 1905. 



Type of genus. — Xenos vesparum Rossi (1790). 



Name derived from Hvoc- (strange) or £s~tvoc (a guest) . 



Male. — Antennae four-jointed, the third produced laterally, third 

 and fourth tapering; tarsi four-jointed; wings having eight primary 

 veins from base, with two distal unattached veins between the radius 

 and medius. 



Female. — Cephalothorax rounded, broadly at sides, narrowly in 

 front. Abdomen with four median genital tubes, on the second to 

 fifth segments. Head short at middle, longer at sides; mouth about 

 middle of ventral side, with mandibles on each side, about half way 

 to lateral margins. This brief description is derived from Nassonow's 

 excellent plate of Xenos vesparum (Nassonow, 1892 c, pi. 1, figs. 1, 

 4, 9, 14). 



Triungulinid : Robust, broadest at mesothorax. Base of head 

 broader than contiguous portion of prothorax. Tarsus of first two 

 pairs of legs rounded pad like, of third pair long, acute. Ninth lateral 



