200 Proceedings of the Biological Society of Washington. 



3. Yellow bands on third and fourth abdominal segments extend- 



ing over the sides 4. 



Yellow bands not reaching the side margins opinator O. S. 



4. The pile on scutellum rather sparse; female with dark rings on 



hind femora just beyond middle; rather small species . rectus 0. S. 

 Pile on scutellum rather dense; female without infuscate rings 



on hind femora ; larger species 5. 



5. No dark median vitta on face ribesii Linne. 



With dark median vitta on face ribesii vittafrons n. var. 



Syrphus knabi new species. 



Squamae with rather long, light yellow pile ; ground color of the sides 

 of thorax bright yellow, with yellow pile; bands on the third and fourth 

 abdominal segments entire and extending over the margins almost in 

 their full width. 



Male: Frons yellow with bluish green reflection, a black spot above 

 each antenna, and with fine rather long, black hairs which continue a 

 short distance down between the antennae and eyes. First two antennal 

 joints reddish brown, the third joint darker, reddish beneath and some- 

 what pointed apically ; arista brownish, a little longer than antenna. 

 Face and cheeks yellow and with light pile. Mesonotum greenish aeneous 

 with two obvious median stripes and bright yellow sides clothed with 

 light golden pile; pleurae a somewhat lighter yellow than the lateral 

 stripes of dorsum, and with golden pile; scutellum yellow with a greenish 

 sheen and with black pile, the sides with yellow pile. Band on the second 

 abdominal segment interrupted and outwardly produced forward where 

 it extends over the sides and up onto the sides of the first segment. The 

 bands on the third and fourth segments run straight across, extending 

 over the sides in almost their full width. Fore coxae and trochanters 

 cinereous, the hind trochanters yellowish, front and middle legs entirely 

 yellow; hind pair yellow, the femora with dark band beyond the middle, 

 yellow posteriorly; hind tibiae darkened on outer side of apical half and 

 clothed with black pile; last four tarsal joints darkened. Length about 

 11.5 mm. ; wing about 11 mm. 



Female : Width of frons at vertex about equal to length of third anten- 

 nal joint, but widening quite rapidly down to the antennae. Frons 

 yellow, brightly so for about one-fourth its extent above antennae, above 

 this a region with a greenish-black reflection which has an ill-defined 

 triangular mark; the last section, which includes the ocelli, is nearly as 

 long as broad and is shining black ; a black spot above each antenna. 



Type locality : Plummers Id. , Md. (Male type, July 19, R. C. Shannon); 

 female allotype. Falls Church, Va. , June 21 (F. Knab). Paratypes are 

 from Plummers Id. , Md. ; Difficult Run, and Dead Run, Fairfax Co. , Va. ; 

 and North Carolina. For the records of locally collected specimens 

 all of which may be considered paratypes, see pp. 182-183. 



Type: Cat. No. 20285, U. S. N. M. 



This species, of which a series of 28 specimens is before me, has been 



