OSTEN SACKEN ON WESTERN DIPTERA. 261 



vous scales, more whitish on the anterior part of the femora. Halteres 

 reddish-yellow. Length 10-ll mm . 



J£ab. — Crafton, near San Bernardino, Cal., in March; San Eafael, 

 Cal., and Sonoma County, in April and May. Much less common than 

 P. nigripennis. Three males and one female. 



This species, in several respects, is peculiar. The marginal cell is 

 unusually short, reaching very little beyond the tip of the first vein, and 

 not expanded at the end, as in all the other species. The consequence 

 is that the submarginal cells have a shape different from the usual one : 

 the first outer submarginal cell is larger, the inner submarginal broader 

 toward the end. The structure of the antennae is peculiar in the shape 

 of the second joint, which is about as long as the third. The rather 

 slender abdomen has none of the dense fringe of pile along the lateral 

 edges, which distinguishes most of the following species. 



2. Ploas rufula n. sp., <?. — Second antennal joint less than half the 

 length of the first; two basal joints beset with long black pile; the 

 under side of the head, occiput, thorax above and on the sides, and 

 the abdomen beset with rufous pile ; conspicuous tufts of black pile on 

 the sides of the three penultimate abdominal segments ; ground-color 

 of the abdomen black, opaque on the two first segments ; the other seg- 

 ments are shining greenish -black, with a small black opaque triangle in 

 the middle and a narrow opaque cross-band at the base. Halteres red- 

 dish-yellow; legs black, beset with fulvous scales and pile, principally 

 on the femora ; spines on the tibiae black ; wings grayish, infuscated at 

 base and along the fore border as far as the end of the first vein and 

 including the first basal cell ; the brown gradually evanescent ; small 

 cross- vein with a deep brown cloud; posterior cross vein with a weaker 

 one. Length ll-12 mm . 



Sab. — San Geronimo, Marin County, Cal., April 19. Two males. 

 In one of them, the cross- vein separating the second outer submarginal 

 cell from the inner one is wanting on both wings. 



5. Ploas nigripennis Loew, Centur., x, 45. — This is the most com- 

 mon Californian Ploas. I have numerous specimens of both sexes from 

 Crafton, near San Bernardino, in March; Marin and Sonoma Coun- 

 ties,jin April and May; Yosemite Valley, in June; Webber Lake, Sierra 

 Nevada, in July. Dr. Loew describes the female. In the male, the 

 opaque spaces in the middle of the third and following abdominal seg- 

 ments are much broader. 



4. Ploas atratula Loew, Centur., x, 44. — I refer to this species, 

 with a doubt, two female specimens taken by me near the Geysers, 

 Sonoma County, California, in May. 



5. Ploas obesula Loew, Centur., x, 46. — California. Two male 

 specimens, received from Mr. H. Edwards, without indication of the pre- 

 cise locality, I unhesitatingly refer to this species. 



6. Ploas amabilis n. sp., $ 9 . — Head black, beset with black pile, 

 except on the occiput, where it is yellow ; the front of the female, be- 



