1911] Aldrich — North American Species of Hydrophorus 69 



larger facets just below the antennse; antennae of medium size, not quite so short 

 as in some species, arista rather long. Dorsum of thorax sealbrown in front, green 

 behind; four scutellars, two humerals, dorsocentrals of moderate size, the hind 

 ones rather strong; pleurae wholly white pruinose, bare, propleura with white hairs 

 and one black bristle; squama blackish with pale hairs; halteres yellow with brown 

 spot on knob and brown root. Front coxae white pruinose and with fine soft hair, 

 at tip sometimes with a few small black spines, sometimes without these; front 

 femur with an irregular row of spines below, larger and smaller mixed and toward 

 the tip on the inner side two or three longer ones; front tibia straight, with a uni- 

 form row of nearly erect, even, small spines on inner side; middle femora long and 

 slender, a little bowed; hind femora also long, not so slender, beyond the middle 

 with numerous dense, curved bristles below; the femur tapers rapidly near the 

 tip, almost excised below; all the claws and pul villi small. Wing narrow, almost 

 hyaline, unspotted, veins blackish. Abdomen bright green, with two long, browni.sh 

 lamellae projecting forward underneath, about half as long as the abdomen; fourth 

 sternite bent forward in a V-shape. Length, 3.2 mm.; of wing, 4 mm. 



Female. Face wider than in male, but still narrowed below the antennae; about 

 fifteen postorbitals on a side; hairs on palpi blackish; a few pale microscopic hairs 

 on sternopleura. Length, 4.9 mm.; of wing, 5.4 mm. 



Forty specimens, both sexes: Craig's Mt. Idaho (type), 

 June, 1894; Moscow, Idaho, May 3, 1895; Potlatch, Idaho, 

 June 20, 1907; Troy, Idaho, Sept. 26, 1896; Harrison and JuUa- 

 etta, Idaho, and Pullman and Seattle, Wash. 



This appears to be the commonest Hydrophorus of the Pacific 

 Northwest. 



Walker's Species. 



Under the name of chrysologus on a preceding page I have 

 described a species which may be the one to which Walker gave 

 that name, although there is no great certainty about the matter. 

 His description of glaber offers no characters of significance differ- 

 ent from that of chrysologus, except that in the former case he 

 mentions the dark knob of the halteres, while in the latter he 

 calls the halteres yellow, very possibly overlooking an infuscation 

 of the knob. The two spots on the wing occur in both descrip- 

 tions, and witli the item about the halteres include almost all 

 of distinctive importance. I know no spotted-winged species 

 with wholly yellow halteres, though in phoca the question is 

 yet open, owing to the loss of both halteres in the single described 

 specimen. If the face is shining in chrysologus, it might be the 

 ' same as algens, but the ambiguous expression used seems to 

 indicate an opaque face: "head covered with golden bloom, 



