24 PROCEEDINGS OF THE NATIONAL MUSEUM vol.74 



KEIROSOMA, new genus 



This would come near Nematoproctus, from which it differs in hav- 

 ing the abdomen compressed and cut off abruptly at tip, in the male 

 at least. The first antennal joint is bare above; arista dorsal; third 

 antennal joint formed as in Nemato'proctus^ the thorax also of the 

 same bright green color, with silvery-white pollen along the front. 

 Bristles on the posterior margins of the abdominal segments very 

 strong; hypopygium concealed, or mostly so, its appendanges rather 

 short, not filiform as in Nematoproctus; wings rather wide; cross 

 vein slightly beyond the middle of the wing and not as long as last 

 section of fifth vein; sixth vein strong but not reaching the wing 

 margin ; third and fourth veins nearly parallel, but slightly divergent 

 at their tips; first joint of hind tarsi shorter than second. 



This would run to Ghrysotus in tables of species ; it differs in being 

 large, very bristly, with the abdomen compressed, cut off squarely at 

 tip, not at all tapering in the male ; the cross vein is beyond the mid- 

 dle of the wing, not before the middle, as in Ghrysotus; the tip of 

 fourth vein is a little beyond the apex of the wing. 



The name has reference to the truncated abdomen of the male. 



Genotype. — Keirosoina aZbicinctuTn, new species. 



KEIROSOMA ALBICINCTUM, new species 



Male. — Length 6 mm. ; of wing 5 mm. Eyes touching for a short 

 distance below the middle of the face, the slender triangle above and 

 short line below silvery white; palpi small, yellowish brown; front 

 shining green; antennae (fig. 75) short, yellow, brown at tip, placed 

 at upper fifth of eye height; orbital cilia short, wholly black; one 

 pair of short post- vertical bristles; one pair of long ocellar bristles 

 curving backward; and one pair of orbital bristles curving inward 

 and forward, crossing each other before their tips. 



Dorsum of thorax shining green with blue and bronze reflections 

 and silvery white pollen along the front; pleurae more black with 

 gray pollen; acrostichal bristles in two rows, rather large; five dor- 

 socental bristles on each side, the anterior one stout but not long, 

 they become long posteriorly ; scutellum large, somewhat truncate at 

 tip, green with violet in the middle, one pair of very large marginal 

 bristles. Abdomen compressed, cut off abruptly at tip (fig. 76), 

 five visible segments, which are blackish purple with a rather narrow 

 green base and some green reflections on the purple portion ; the green 

 base is opaque with white pollen when viewed from above, this white 

 pollen narrowly interrupted on the middle of the dorsum ; posterior 

 margin of all segments with a row of very long bristles; all hairs 

 and bristles of thorax, abdomen, legs, and feet black. 



