324 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lo* 



3.9 mm. ; wings equal to, slightly shorter than, or longer than the body, 

 1 .8 to 2.8 times as long as broad. Head generally wider than length or 

 height and higher than long. Upper half of postcranium with the 

 cerebral plate concave in profile, inferior margin of cerebral plate raised 

 and slightly prominent, lower part of postcranium more or less con- 

 vex. Eyes in profile shorter or longer oval, with axis nearly vertical 

 in nearly all species examined ; with sparse, erect whitish microscopical 

 hairs in the larger species, apparently bare in the smaller species; 

 ratio of height to width of eye in profile 1.3 to 2.4. Genae below eyes 

 in most species very narrow, usually one-half as wide to wider than 

 postpedicel. Frons at vertex always more or less wider than one eye 

 and usually slightly shorter than width at vertex (measured from 

 lunula to vertex in the median line); flattened, slightly produced near 

 antennae and gradually narrowed to anterior margin. Mesofacial 

 plate (face) sunken, not visible in profile, slightly receding beneath, 

 with indistinct and superficial antennal fovae, oral margin raised and 

 more or less prominent. Head in all species yellow, without black 

 spots, genae slightly darkened below the eyes in some species; with or 

 without conspicuous pruinosity; mesofacial plate may be evenly and 

 densely dusted in some species. Only four of the known species have 

 frons distinctly vittate by pruinosity; lateral borders of frons along 

 eyes and a median vitta along frontal stripe in these species densely 

 white pruinose, the bare parts of frontal stripe forming two broader, 

 intensive, testaceous to reddish yellow vittae. Antennae and mouth- 

 parts as yellow as other regions of head, except for the mostly brown 

 labella. Scape of antenna very short; pedicel with some short and 

 thickish hairs and with conspicuous dorsal bristle. Postpedicel short- 

 lobate, with widely rounded, truncated apex, 1.1 to 2.2 times as long 

 as wide and slightly shorter than mesofacial plate. Shape of maxillary 

 palpi variable in the genus but constant as a specific character, dis- 

 tinctive in being slightly curved and broadly sickle-shaped, although 

 in some species it is oval and not curved and with a differently formed 

 apex. Prementum very short and small, yellow. Cephalic bristles 

 somewhat flattened, usually brownish yellow but genal bristle (ge) 

 mostly darker in color. Usually three pairs of convergent lower orbital 

 bristles (on), anterior pair usually shorter than posterior pairs but in 

 some forms all three pairs subequal in length. Two pairs of recurved 

 upper orbitals {ors)^ posterior pair shorter and weaker than anterior. 

 One pair of divergent ocellars {pc), usually long and robust. Outer 

 pair of divergent verticals {vte) more or less shorter than inner pair 

 {vti)y the longest and strongest of the cephalic bristles. Postverticals 

 ijpvt) parallel and relatively short. 



Body yellow in ground color with conspicuous black markings on 

 thorax and abdomen; spots may occasionally vary in size and color 



