AMERICAN DIPTERA. 273 



ing the species heretofore described ; but will serve, at least, 

 as a fairly good guide to the known species of this family in- 

 habiting North America. In the compilation of this synopsis 

 only those characters which seem the least variable and most 

 conspicuous are used. No attempt is made towards a seri- 

 ous classification. 



The flies of this family are small, nearly bare, except Ver- 

 rallia, black, with at most only the humeri, halteres, the sides 

 of the abdomen rarely, and the legs, yellow; more or less 

 variegated in appearance by the presence of silvery pubes- 

 cence on the front and face, and gray or brown pollinose 

 coating on the bodies and legs. The surfaces are generally 

 shining, being more or less obscured by the density of the 

 pollen, so that rubbed specimens are more shining than 

 normal ; the abdomen is sometimes semi-shining, as it were, 

 caused by the minute granulation or rugulosity of the sur- 

 face. The color of the humeri is a very good character, but 

 close examination is necessary on account of their being 

 covered by the swollen occiput, or, rarely, the color is diffi- 

 cult to distinguish between a brown and yellow. 



The head is large, unusually so, larger than the thorax, 

 especially in the genus Pipunculus ; composed mostly of the 

 compound eyes, leaving the narrow face and front ; the latter, 

 in the male reduced to a small triangle by the contiguous, 

 rarely narrowly separated, eyes. Antennae situated about 

 on line with the middle of the head, composed of a small 

 second joint and an elongate, pendant, third, which is more 

 or less acute or acuminate apically, bearing near its base 

 above, a simple, naked, hair-like arista, which is more or less 

 thickened basally. The mouth parts are generally retracted, 

 but sometimes the small, clavate palpi are visible. The 

 thorax is smaller than the head,. quadrate, with the mesono- 

 tum and scutellum rarely with regularly arranged series of 

 fine bristles ; humeri well developed, sometimes appearing 

 like scales. Abdomen ovate and flattened, or narrow and 

 subcylindrical, consisting of five segments in the male and 

 six in the female. Legs generally moderately slender, with 

 apical portion of the femora and tibiae more or less thick- 

 ened, without distinct bristles, except the femoral spines, 



TRANS. AM. ENT. SOC, XXXVI. (35) DECEMBER, 1910. 



