Williston.] ^-^^ [May 19, 



h. — Face descending but very little below the eyes, arched 

 or subcarinate, never tuberculate. 

 i. — Tliird segment of abdomen in male very much con- 

 tracted, cylindrical, the hind femora much swollen, 

 ■with bifid spine below at the tip. Eyes very large, 

 fece small Senogaster Macq., Hist. Xat. Dipt. 2. 



Senogaster Comstocki, sp. nov. 



(J-. — Head globular, large, composed almost wholly of the ej'es which 

 meet in front for a short distance above the antennae, the vertical triangle 

 narrow, long ; a small but very distinct area of enlarged facets on each 

 side above the antennae. Frontal triangle and face small, the latter 

 arched, subcarinate, short, concave from antennae to tip, yellow with sil- 

 very glisten, and a brownish median stripe. Cheeks narrow, antennae 

 reddish-yellow, first joint very short, second nearly equilaterally triangu- 

 lar, third joint oval, arista bare. Thorax black, with four narrow, but 

 conspicuous olivaceous stripes, the outer pair extending from the more 

 reddish, somewhat swollen humeri. Pleurae black, with a conspicuous 

 broad white-dusted vertical patch ; scutellum black, yellow at the tip ; 

 abdomen brownish-black ; first segment as broad as thorax, nearly black, 

 yellow on the sides ; second segment elongate, scarcely half as wide be- 

 hind, with two silvery elongate spots ; third segment of the same length, 

 narrow, cylindrical, yellow in front ; fourth segment as long as preceding, 

 with the globular hypopygium forming a spheroidal mass. Legs yellow, 

 hind femora much swollen, arcuated, black, becoming red at the tip, be- 

 low at the end with slender process, and beyond a smaller tooth-like one, 

 hind tibiaj arcuated with a triangular projection at the end, hind tarsi 

 brownish, wings nearly hyaline, third longitudinal vein gently curved. 

 Long. corp. 12 mm., long. al. 8 mm., N. Y., Cornell University. Prof. 

 J. H. Comstock. 



The present species is a very interesting addition to our fauna. Hitherto, 

 so far as I can learn, but one species is known, S. cxrulescens Mac, 1. c. 

 and Dipt. Exot. 11, 2, 72, Tab. 13, f. 3, from Guiana, South America. I 

 take much pleasure in dedicating it to Prof Comstock, whose work in 

 Entomology is so favorably known. 



ii. — Hind femora more or less swollen with spines or bristles below, abdo- 

 men elongated, somewhat flattened, not contracted in the middle. 

 Thorax without distinct yellow markings. 

 j. — Hind femora very much swollen ; small cross-vein at right atigles 

 to longitudinal veins Syritta. 



Syritta nriENS Linne. Meigen Zweifl. Ins. iii, 213. Europe. Com- 

 mon apparently over all of North America. 



jj. — Hind femora never remarkably swollen, hind co.xjt; often with a 

 spinous process, small cross vein of wing always oblique. . .Xylota. 



Xylota obscura Lw., Cent, vi, 55. Mt. Hood, Oregon ; Wash. Terr. 

 Calif. ! Red River of the North. Specimens from the former localities 



