Art. 4. REVISION OF THE FAMILY THEREVIDAE—COLE. plalee 
which is difficult to work out without extensive collecting; we see 
such a group around Villa (Anthrax) alpha in the Bombylidae, and 
we have the old problem of distinguishing between species, subspecies, 
and races or varieties. 
In the forms related to Thereva comata the external male genitalia 
are apparently identical and the differences are more of coloration 
than structure. In some specimens there are six to eight strong 
bristles on the outside of the hind femora and in others there are 
fewer or none. The tips of the femora are reddish in some, and three 
specimens, possibly distinct species, from the Sierra Nevada Moun- 
tains in California (Hy. Edwards), [Amer. Mus.], have the femora 
and the pile of the body largely yellow; there is a narrow black band 
across the frons of the female and the hind femora lack the bristles 
on the outside. Specimens from Pismo and San Miguel Island, Cali- 
fornia, possibly form a distinct subspecies or race; they have more 
black pile on the body than the others, entirely black femora, the 
tereum of the abdomen largely dull black, without pollen, and the 
venter gray pollinose. 
Krober describes comata as having pollinose bands on the abdomen 
in addition to the yellowish incisures. I have examined a series of 
18 specimens of what I take to be the typical form and in these the 
venter is gray pollinose. The male genitalia are small, the hypan- 
drium much reduced and with yellow pile. ‘The fourth to seventh 
tergites of the male abdomen have more or less brownish yellow pol- 
len on the posterior borders; in the female the fourth and fifth abdom- 
inal tergites have gray pollinose borders. The female frons is golden 
yellow pollinose, black pilose, except above the antennae, and with a 
narrow shining black band interrupted in the middle by the yellowish 
pollen. 
Specimens examined.—22 males, 5 females. 
Washington: Wawawai, July 8 (R. C. Shannon), [Shannon]. 
California: Stanford University, May 17 to 25 [Stanford U.]; San 
Francisco (H. Edwards); ‘Cal.’’ (Osten Sacken); [M. C. Z.]; ‘‘Cal.’’ 
(KE. T. Cresson), [A. N.S. P.]; Compton, April 15 (Cole); Stanford 
University, May 15 (Cole), [Cole]; Pismo, April 14 to 25 (i. P. Van 
Duzee); San Miguel Island, April 14 to May 20; Salada Beach, San 
Mateo County, May 25 (KE. P. Van Duzee); Santa Cruz, June 3 (E. 
P. Van Duzee); sand dunes near San Francisco, May 31 (C. L. Fox); 
San Francisco, April 11 (C. L. Fox), [all Cal. Acad. Sci.]; Pasadena, 
{U.S.N.M.]. 
THEREVA NEBULOSA Krober. 
1912. Thereva nebulosa KréseEn, Stett. Ent. Zeit., p. 264. 
Type locality.—California. 
Type:—In the collection of Kréber. 
