March, igio.J OSBURN : STUDIES ON SyRPHID^. 53 



STUDIES ON SYRPHID^.— I. SYRPHUS ARCUATUS 

 FALLEN AND A RELATED NEW SPECIES. 



By Raymond C. Osburn, 



Columbia University, New York City. 



(With Plate I.) 



Concerning the species Syrphus arcuatus Fallen there has always 

 been much confusion. Not only have the color variations, which 

 here have a wide range, given rise to a number of synonyms, but 

 the species has been confused with other members of the genus. A 

 number of years ago the writer began collecting material in order to 

 study the species, and, while examining a male of what I had sup- 

 posed was arcuatus, I was much surprised to find an area of enlarged 

 facets on the eye as in the Catabom.bas. Examination of the rest 

 of my collection at once revealed several more males in the same 

 condition. When I attempted to remove these from arcuatus I found 

 that some of them had a strongly curved third vein, while others 

 had this vein straight. Here was more trouble, for Williston (Syn. 

 N. A. Syrphid?e, pp. 68-9) had made use of this difference in venation 

 as the basis for his two varieties arcuatus and lapponicus. The fol- 

 lowing dilemma now presented itself: if I separated the males by 

 means of the eye characters (a supposed generic difference separating 

 Catabomba from Syrphus) some of either lot had curved veins and 

 I could not separate the females at all; if I separated them on the 

 basis of the venation the females could be placed as readily as the 

 males, but in each group some of the males had the area of enlarged 

 facets and some lacked it. A careful examination of my material 

 of both sexes revealed a number of minor differences correlated with 

 the venational differences but none with the differences in the eye 

 facets. 



Not being satisfied with the study of my own material merely, 

 I obtained the loan of specimens from many American dipterologists 

 as well as all those in the U. S. National Museum and the American 

 Museum of Natural History, and a number of specimens from 

 Europe. My thanks are due for the loan of material and for other 

 assistance to Messrs. S. W. Williston, C. W. Johnson. Jas. S. Hine, 



