1911] Aldrich— North American Species of Hydrophorus 61 



Twenty-five specimens: Mt. Rainier, Wash., above Longmire's 

 Springs, Aug. 3, 1905, and Marshall Pass, Colo., July 28, 1908. 

 Compared with cotypes loaned me by the American Museum 

 of Natural History, 



I was in doubt about the identification until I had examined 

 the cotypes, as in my material the costa is not yellow so far 

 from the base as in Wheeler's. 



Hydrophorus signiferus Coquillett. 



(Copy of original description.) 



Female. Upper part of the occiput, front and face opaque, densely brownish- 

 yellow pruinose, a small gray spot below each of the facial tubercles; palpi brownish- 

 yellow pruinose in the center, the edges gray; proboscis and antennae black, third 

 joint of the latter subquadrate, slightly broader than long; a notch at insertion of 

 the arista and another opposite it on the lower side of the joint; penultimate joint 

 of arista one-half as long as the last joint; bristles of occiput black, intermixed with 

 a few pale yellow hairs. Thorax blackish, the margins and upper part of the 

 pleura opaque, densely brownish-yellow pruinose (center of the dorsum may have 

 been abraded in the single specimen before me), remainder of pleura white pruinose; 

 scutellum opaque, densely brownish-yellow pruinose, bearing four bristles. Abdo- 

 men shining bronze green, the lateral margins and venter white pruinose. Coxse 

 and trochanters densely whitish pruinose, femora and tibiae shining, bronze green, 

 the tarsi black; front femora bearing a few short spines on the basal third of the 

 under side. Wings grayish-hyaline, veins bordered with pale brown, a dark brown 

 spot on the hind crossvein and another near the middle of the last section of the 

 fourth vein; third vein toward its apex strongly curving toward the fourth; hairs of 

 lower calypters pale yellow. Halteres yellowish, the knobs brown. Length, 6 

 mm. 



Type.— No. 4052, U. S. N. M. 



Bering Island, July-August, 1897. A single specimen collected 

 by Mr. Barrett-Hamilton. 



Hydrophorus algens Wheeler. 

 Face rather wide in both sexes, only moderately narrowed above, bulging and then 

 receding below, with brownish-yellow dust, which is denser in the male, allowing 

 nothing of the ground-color to be seen; in the female however the metallic blue-green 

 color shows through, but is not very bright. Palpi with brown dust and mostly 

 yellow hairs; front opaque brown; postorbital black bristles in a rather dense row, 

 beard yellow; postvertical bristles only one pair. Thorax with thin seal-brown 

 pruinosity extending down to the middle of the pleura, where it changes suddenly 

 (viewed from in front) into glaucous; dorsocentral and acrostichal bristles erect, 

 long and slender, about 10 dc in a row. A lighter color in spots between these 

 bristles (in the row) gives the effect of three paler lines on the dorsum; four strong 

 scutellars; propleural one, among yellow hairs; halteres dark brown, stem yellow. 



