174 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Abdomen smooth, sub-opaque, dark gray, with slightly silky surface, 

 rather long and with parallel sides; second, third, and fourth segments of 

 equal length, each more than half the first; the hairs on hind edge are 

 longer and more numerous on each succeeding segment, very striking on 

 the last, yet so slender as hardly to be called bristles; fifth tergite con- 

 spicuous, half as wide in middle as the preceding, unsymmetrical in shape, 

 its left end shortened and exposed, the right passing out of sight under the 

 preceding segment; its hind part bearing long, rather appressed hair; first 

 segment of hypopygium rather large, with the same hair; second segment 

 large but more or less folded in out of sight, its hind part bearing an 

 unsymmetrical black hump or protuberance to the right of the middle; a 

 fringe of black hairs around the nearly circular anal space ; the inner for- 

 ceps forming an oblong plate with only short projecting anterior outer 

 angles ; outer forceps shining yellow to brown, very slender and nearly 

 straight, far apart at base but approaching apically, the tips slightly turned 

 up ; anterior claspers a little larger than the outer forceps, shining yellow, 

 strongly curved forv/ard, widened near apex; fifth sternite broadly shining 

 black in middle, the sides opaque, both parts hairy, lobes with longer hair ; 

 fourth sternite large, prominent, hairy. 



Legs entirely black; front tibia with one bristle in front; middle tibia 

 with two on outer front, two on outer hind, one on inner hind side ; hind 

 tibia with three behind (the middle one long and tapering), three on 

 outer hind, four on outer front ; middle femur with row of small bristles 

 on lower front edge and another a little larger but still small on lower hind 

 edge; outer side of hind femur with the usual row above, and a row of 

 about a dozen below, beginning near base. Claws large, pulvilli hardly en- 

 larged. Hind basitarsus without spine below. 



Wings uniformly subinfuscated, veins heavy and dark; costa broken at 

 tip of first vein, which is pale for a short distance ; first vein almost white 

 for a section near its middle, thence to apex heavy and black ; some in- 

 distinct pale markings around the basal crossveins ; costal spines very 

 minute, no setules before or beyond them. 



Female: Front .461 of head-width (in allotype) ; ant acr in the middle of 

 the series coarser than in male ; middle tibia with two on inner front, none 

 on inner hind, two on outer front, two on outer hind ; middle femur with 

 the bristles on lower front edge larger than in male, second segment of ab- 

 domen shortest, fourth narrowing almost to a point, and bearing at hind 

 edge both above and below a close row of stout, appressed bristles, about 

 16 above and 12 below ; other abdominal bristles inconspicuous ; lateral and 

 lower surface of abdominal tergites and whole of sternites covered with 

 short, erect, spiny hairs of an unusual character. The rest as in male. 



Length 5>4 to 63^ mm. 



Twelve males and four females, collected by Dr. Barton 

 Warren Evermann, Director of the Museum of the California 

 Academy of Sciences, for whom the species is named, on the 

 Farallon Islands off the Golden Gate, on July 6, 1917. "This 

 kelp-fly is excessively abundant on the Farallon Islands. On 

 July 6 and again on August 6, 1917, when I visited Southeast 

 Farallon Island, these flies simply swarmed by hundreds of 

 millions on and about the bird rookeries, particularly on the 

 areas where Brandt's cormorants were nesting. One could not 

 move about these rookeries without being constantly covered 

 and surrounded by myriads of these pestiferous little flies." 

 (Evermann.) One female from the Museum of Comparative 



