Dec, 1904.] Tabinidae. 229 



Si L VI us Meigen. 



Members of this genus are widely distributed, being found on 

 nearly all the large land areas of the globe. Our three species 

 are western, none of them having been taken on the Atlantic 

 coast, but quadrivittatus has been collected several times on the 

 gulf coast of Texas. In North America the genus is divided into 

 two distinct groups, gigantulus belonging to one and the remain- 

 ing species to the other. The following key is offered as an aid 

 in separating them: 



1. Wings hyaline, without spots, yellowish along the costa; whole 



body yellowish giga)ituliis 



Wings hyaline, usually spotted; whole body gray poUinose 2 



2. Abdomen above with four longitudinal rows of spots quadrivittatus 

 Abdomen above with two longitudinal rows of spots or 



none pollinosus 



Silvius gigantulus Loew. Length 10 to 13 millimeters. 

 Although this one is very distinct in coloration from the other 

 American species of the genus the generic characters are the same 

 in all. It has the appearance of vituli of Europe, the wings are 

 uniformly colored, being hyaline with the exception of the costal 

 border which is yellowish, the antennae are yellowish with the 

 third segment except the extreme base dark brown, two small 

 spots on the face, a triangular frontal callosity and ocelli dark 

 brown, remainder of the face and front, rear of the head, and. 

 thorax covered with yellow^ pollen and yellow pile. The abdo- 

 men is yellow with a dark spot beneath the scutellum and a spot 

 of the same color on the anterior middle of the second segment 

 and in some specimens there is an irregular middorsal black 

 stripe running the whole length of the abdomen. The male is 

 colored like the female. 



Silvius pollinosis Williston. The specimens that fall in this 

 and quadrivittatus are variable and it is usually a difficult matter 

 to make satisfactory determinations. The character which I 

 have given in the key above, namely: the arrangement of the 

 dark coloration on the abdomen may be used but even this is 

 variable. In this one the color may be in two series, or these 

 two series may be united to form a middorsal rather wide band, 

 or lacking altogether. In some specimens the abdomen is yellow 

 on the sides and in others not. The wings usually have prom- 

 inent black markings on the cross-veins and at the furcation of 

 the third vein and the stigma is black. The male is colored like 

 the other sex, and has as many variations, although it appears to 

 be more often yellow on the sides of the abdomen. Length 8 to 

 11 millimeters. Type from western Kansas. 



Silvius quadrivittatus Say. This species was placed in the 

 genus Chrysops when its description was written by Say and was 

 not recognized by Osten Sacken when he published his Prodrome, 



