Dec., 1904.] 
Tabjiiidae. 
229 
SiLVius Meigen. 
Members of this genus are widely distributed, being found on 
nearlv 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 ' gigantulus 
Wings hyaline, usually spotted ; whole body gray pollinose 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 ajjpearance of vituli of Europe, the wings are 
uniformlv colored, being hyaline with the exception of the costal 
border which is vellowish, 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, 
