ART. 4, REVISION OF THE FAMILY THEREVIDAE—COLE. 85 
California: San Francisco, March 26 to April 19 (I. C. Van Dyke), 
|Cal. Acad. Sci.]; ‘‘Cal.’’ (Edwards), [Amer. Mus.]; La Quinta, San 
Bernardino County, April (Cole), [Cole]. 
Genus THEREVA Latreille. 
1796. Thereva LATREILLE, Precis Caract. gener. Ins., p. 167. 
1775. Bibio Fasrictus (not Geoffroy), Syst. Ent., p. 756. 
1840. Exopata Macquart, Dipt. Exot., vol. 2, p. 76. 
Thereva LoEw and many other authors. 
Very nearly like Psilocephala, usually larger and more thickly pi- 
lose, the main distinguishing character being the hairiness of the face; 
the head is of much the same shape as Psilocephala. The frons of 
the male is usually thickly pilose and in both sexes the face, cheeks, 
and occiput are pilose, often densely so in the male; in many species 
the frons of the female offers good specific characters, having velvety 
black or shining black marks or callosities which vary greatly in 
shape and size. The antennae do not vary so greatly in shape as in 
Psilocephala and are always shorter than the head, the color usually 
being constant and of specific importance; the basal joint is rather 
long and cylindrical, never greatly inflated, with some pile and with 
bristles on the apical portion; second joint short and with short pile; 
the third joint divergent, about as long as the first, with the appear- 
ance of an annulation at the base, with no pile and with a short 
apical style, at the end of which there is a very short bristle. 
The thorax is about as in Psilocephala, often densely pilose in the 
male; the thoracic bristles arranged in about the same manner as 
in Psilocephala. There are two pairs of marginal bristles on the 
scutellum. 
The abdomen is conical and longer than the thorax, with seven or 
eight obvious segments in the male, the eighth segment in the female 
being the base of the ovipositor. The dorsum of the abdomen is 
never flattened and densely silvery pollinose as in many species of 
Psilocephala, with the exception of one aberrant species. The male 
genitalia are distinct, but do not show the unusual development found 
in some of the other genera and are proportionately rather small; in 
some species that are well differentiated in other ways the external 
male genitalia are apparently the same in structure. 
The legs are much the same as in Psilocephala, but in most species 
with more bristles; in the males the femora often long dense pilose; 
the bristles of the hind femora form an irregular antero-ventral row 
of about seven; the bristles of the tibiae arranged about as in Psilo- 
cephala—three rows of three to six bristles on the front, four rows of 
four to seven on the middle, and four rows of about eight on the hind 
tibiae. There is some specific and some individual variation. 
