24 STREPSIPTERA 



ic. Parasites of Lamdae 3. Tribus Tachytixenini, nov. tribus. 



4a. Males known; parasites of Tachyles 1. Genus Tachytixenos, nov. genus. 



id. Parasites of Sphecidae • . 4. Tribus Ophthai.mochi.ini, Pierce. 



5a. Parasites ofSphex; wings having eight primary vents 

 from base, and with two detached veins between 

 radius and inedius, and one between medius and 



cubitus ,...1. Genus Eupathocera, Pierce. 



5b. Parasites of Chlorion; wings having seven primary 

 veins from base, the third ana! lacking, and with 

 two detached veins between radius and medius, and 



one between medius and cubitus 2. Genus Ophthalmochlus, Pierce. 



5c. Parasites of Scclifhron 3. Genus Sceliphronechthrus, Pierce. 



ie. Parasites of Bembecidae 5. Tribus Paraxenini, Pierce. 



6a. Parasites of Bembecinus. Wings with eight primary 

 veins from base, and with two detached veins 

 between radius and medius 1. Genus Pakaxenos, Saunders. 



I. Tribus XENINI, Pierce 



Xenides. Saunders, Trans. Ent. Soc. Lond. p. 35 (1872). 

 Xenini. Pierce, Bull. U. S. Nat. Mus. no. 66, p. 116(1909). 



Characters. — Male. — Metathoracic praescutum keystone-shape, strongly convex in front; 

 scuti very narrowly separated by scutellum, but not locking it; postlumbium more than twice as wide as 

 long; postscutellum elongate, sides not parallel be3'ond middle, converging to a narrowly rounded apex. 



Female. — Cephalothorax usually heavily pigmented at base, and not with lighter spot over 

 spiracles; cephalothorax at spiracles 1.17 to 1.46 times wider than head at base; head 3.36 to 4.68 times 

 wider than distance between mandibles. 



The tribe is formed to contain the three genera parasitic on Vespidae. 



I. Genus XENOS, Rossi 



Xenos. Rossi, Fauna Etrusca, Mant. Ins. App. p. 114(1790); Kirbv, Trans. Linn. Sue. Lond. Vol. 11, 



pp. 1 1 3- 1 16 (i8i3); Saunders, Trans. Ent. Soc. Lond. p. 37 (1872). 

 Xenus. Rye, Zool. Record. Vol. 10. p. 2g3 (1875). 

 Acroschismus. Pierce, Proc. Ent. Soc. Wash. Vol. 9, p. 79 (1908). 

 Schistosiphon. Pierce, ibidem, p. 80 (1908). 



Xenos. Pierce, Bull. U. S. Nat. Mus. no. 66, pp. 116, 117 (1909). 

 Acroschismus. Pierce, ibidem, pp. 1 19-122 (1909). 

 Schistosiphon. Pierce, ibidem, pp. i32, 1 33 (1909). 

 Xenos. Pierce, Proc. U. S. Nat. Mus. Vol. 40, p. 497 (191 1). 



Characters. — Male. — Head transverse, eyes prominent, many-facetted. Mandibles slender, 

 sinuate, ensiform, apically acute : maxillae two-jointed, tire second joint usually shorter than the first. 

 Antennae very sensitive, four-jointed, the third laterally produced, the flabelli of third and fourth 



