Banks, Greene, McAtee, and Shannon — Dist. of Col. Diptera. 201 



confused witli ribesii, grossulariae, and xanlhostomus . It differs from 

 ribesii and rectus in its bright yellow mesonotal side margins; apically 

 pointed third antennal joint ; bases of femora in male yellow, and second 

 and third yellow bands of abdomen but little narrowed laterally. It is 

 the only species included in the table having the small bristles on the 

 underside of the middle tarsi yellow instead of black. All the above 

 mentioned specimens agree closely among themselves. Three specimens 

 from Texas agree with this species except for having some black bristles 

 intermixed with the yellow ones on the under side of the middle tarsi and 

 the wings slightly yellowish. 



I desire to express my sincere appreciation of the deep interest taken 

 and helpful suggestions made by Mr. Frederick Knab in the work I have 

 undertaken. Through his critical readings of all the papers I have pre- 

 pared many important changes have been made and faults corrected. It 

 is with great pleasure therefore that I name this species in his honor. 



Syrphus rectus O. S. 



Osten Sacken * in his work ' ' The North American Species of the Grenus 

 Syrphus" described Syrphus rectus from the White Mts., N. H., and 

 New York ; afterwards he placed it as a synonym of ribesii L. In dis- 

 cussing rectus he stated that he had two forms, a small one in which the 

 female has a brown ring on the hind femur, and a larger form the female 

 of which has the hind femora entirely yellow. In studying local material 

 of ribesii and allied species the writer was able to separate a form which 

 agreed with the description Osten Sacken gives for the small variety and 

 with small specimens from the White Mts., N. H. 



Slide mounts of the male genitalia of one of these specimens, a European 

 specimen of ribesii, and a local ribesii, show that the small form is a 

 distict species from ribesii. Upon the advice of Messrs. Knab and Banks, 

 Osten Sacken' s name, rectus, is applied to this species. 



But few characters appear to be available to separate rectus from ribesii. 

 In rectus the pile on the thorax is paler and less dense than in ribesii; 

 and on the scutellum noticeably sparser; the bands on the third and 

 fourth abdominal segments in the female are quite straight and scarcely 

 narrowed at their ends. In the male the yellow markings on this second 

 abdominal segment in the part produced forward to the basal angles are 

 much broader than in the male ribesii. The female of rectus has a dark 

 ring on the hind femur just beyond the middle. Rectus is noticeably 

 smaller than ribesii. 



Length of rectus, male: 8-9 mm., wing 7-8.5 mm.; of female: 8.5-9 

 mm., wing 7.5-9.5 mm. 



Length of ribesii, male: 12-13 mm., wing 10-11.; of female about 13 

 mm., wing 10-11 mm. 



For records of this species in the vicinity of Washington, D. C., see 

 p. 183. Other specimens of this species in the National Collection 

 are from Beverly, Mass. ; White Mts., New Hampshire ; North Carolina; 

 * Proc. Boston Soc. Nat. Hist. XVIII, pp. 135-158, 1875. 



