• AMERICAN DIPTERA. 323 



legs more or less shining ; tarsi always short spinose beneath ; the 

 hind knees of the male with peculiar sexual armament, legs of 

 female simple, not fringed with scales; pulvilli and claws small, 

 the pulvilli dirty white, the claws reddish at the base, black 

 apically. Halteres pale yellow. Wings nearly pure hyaline, the 

 veins strong, dark fuscous, no stigmal spot or with a very faint 

 indication of one, no strong costal bristles. 

 Western species. 



Empis aerobatica sp. nov. 

 Male and Female. Length 5 mm. — Gray-dusted species. Eyes of the male 

 separated twice as widely as the posterior ocelli, of the female scarcely more. 

 Palpi yellow, with one minute hair beneath. First anteunal joint scarcely one 

 and one-half times the length of the second joint. Thoracic vitta; narrow, as 

 broad as the intervittfe, generally well defined, the intervittse gray, with a slight 

 bluish tinge when viewed in a strong light; but one marginal bristle above the 

 base of the wings. Bristles of the occiput, pronotum, humeri, scntellum, abdo- 

 men and legs minute; scutellum with four bristles; about five minute bristles iu 

 front of the halteres, pectus with about three minute bristles on each side. Hy- 

 popygium in part gray-dusted ; central filament gradually narrowed, brown ; 

 upper lamellfe triangular, about two-thirds as large as the middle ones, wholly 

 visible. Coxse more or less darkened at the base, legs fuscous, darker on the 

 femora above and the tibise apically; tarsi short spinose, front and middle ones 

 not enlarged, hind ones moderately thickened ; hind femora not thicker tliaji 

 the tibise, not reaching the hypopyginm, in the male provided with a short diag- 

 onally transverse process, the inner apical angle of which bears a pencil of black 

 hairs, beyond which the inner inferior edge of the femur is ciliate with about 

 four bristles and a few hairs; the base of the tibia bears on the under side two 

 prominent tubercles, the first with a scattered pencil of black bristles, the second 

 with a brush of short hairs on its obliquely truncate apical edge. Wings narrow, 

 clear hyaline, those of the male with a very long base; furcation of the third 

 vein variable, before the end of the marginal cell, or opposite the end, the poste- 

 rior branch terminating near the extreme wing-tip; discal and posterior cells 

 rather elongate, the hind margin of the discal cell about three-fourths the length 

 of the outward continuation of that vein ; anal vein much reduced, sharply 

 vanishing. 



Seven males and four females ; California and Idaho. 



This is the balloon-making fly about which Messrs. Aldrich and 

 Turley have written a most entertaining account in the American 

 Naturalist, 1899. The male forms a large hollow frothy bag, in the 

 front end of which is imprisoned a small fly. Flying with this 

 structure between its hind legs it courts the female who alights on 

 the back of her selected mate. The pair then settle slowly to the 

 ground, and after copulation the male discards the balloon which 

 then has served its purpo.se of attracting the female during courtship. 



TKANS. AM. ENT. SOC, XXYIII. SEPTEMBER, 1902. 



