246 C. T. BRUES, 
the sex of the host is not influenced, or at least only to a slight 
degree by the presence of the Xenos larvae in its body. The sex of 
the parasites does seem, however, to be influenced in some way by 
the individual Polistes in which it occurs. There is a well marked 
tendency for all the parasites in one wasp to develop the same sex. 
The three species of Xenos, of which I have seen specimens, may 
be readily separated by the aid of the following dichotomy. 
North American Species of Xenos. 
Males (winged) . . ER. à © 
Females (wingless, larviform) À 2 
2) Head above!) orange, irregularly blackened posteriorly, the light 
color extending back much further along the median line and 
on each side. Anterior half of thorax strongly fuliginous, its 
lateral wrinkles black . . . - + peck Kırev. 
Head black above, except the anterior third, which is orange, 
the line between the two colors being straight and transverse. 
Anterior half of thorax yellow, its lateral wrinkles ferrug- 
INOUS 0 . … mgrescens N. sp. 
3) Second joint ‘of palpi distinctly. separated from the first joint 
along the entire circumference of its base . pallidus n. sp. 
Second joint of palpi not separated from the first on the ventral 
side, separated dorsally . . ; a SEE 
4) All the wing nervures distinctly dackencd) wings very stout 
peckii Kirpy. 
Wing nervures very weak, posterior ones hardly visible. Wings 
delicate. en “Sa Ge Oe IUT ESCEN SETS 
Xenos pallidus n. sp. (Fig. B, b). 
Male. Length 2.25—2.75 mm. Head and thorax above fuscous, below 
very pale luteous, antennae with the first two joints luteous, the rami 
of the fourth joint yellowish gray, their spots pale. Eyes black, their 
hemispherical facets of the usual size. Mandibles pale luteous, white 
at tip. Palpi white, distinctly two-jointed, the first joint nearly twice 
as long as the second and obliquely truncate at apex; second joint oval. 
Prothorax and mesothorax fuscous; elytra pale, grayish at tip. Dorsal 
sclerites of the metathorax shaped. as in X. peckii; fuscous, darker on 
the post-scutellum. Legs pale luteous, tarsi slightly grayish above near 
tips. Wings pale hyaline, the nervures very delicate and not pigmented 
along their edges. The costal margin darkened for nearly its entire 
length. Abdomen finely transversely wrinkled on the dorsal surface; 
grayish yellow, blackened above, especially posteriorly. Ventral plates 
1) i. e. the side uppermost, morphologically the ventral side. 
