March, 1910.J OSBURN : STUDIES ON SyRPHID^. 69 



the generic descriptions of " Scccva " or " LasiopJithicus " except 

 as modified to include the characters outhned by Osten Sacken for 

 " Catabomba," viz.: (i) Enlarged eye-facets in the male; (2) swollen 

 frons; (3) small hypopygium, to which may be added the following 

 characters more or less correlated with these; (4) pilose eyes; (5) 

 curved third vein. 



The problem resolves itself into this : Are these characters suffi- 

 cient for the separation of a genus? If they were constant no cjie 

 would raise an objection, but right here lies the difficulty, for tht're 

 is not one of them but exists to a greater or less degree in members 

 of the genus Syrphns. In a word, " Scccva " is based on a specialized 

 condition of certain characters which fade out in the various species 

 of Syrphns. Let us examine these characters singly. 



I. Enlarged Facets.— In all species of SyrpJius which I have ex- 

 amined (or in all Syrphidae for that matter), the facets of the upper 

 central part of the eye, in both sexes, are larger than those around 

 the border and upon the lower half of the eye. In most cases there 

 is a regular intergradation in size, but in the males of certain 

 species (pyrastri L., albomaculatus Macq., sclcniticits Meig., mclanos- 

 toma Macq.) there is a sharp line of separation marking ofif the area 

 of enlarged facets from the smaller ones below, behind and before 

 the area (PI. II, Fig. i). This line of demarkation is not always 

 complete (Fig. 2), and Girschner has pointed out* that the amount 

 of separation varies with different species, and has indicated his 

 doubt of the validity of the genus because of this. In this obser- 

 vation Girschner is entirely correct, as I have determined by an 

 examination of pyrastri, albomaculatus and sclcniticiis, and there 

 is also more or less individual variation in pyrastri (my series is not 

 large enough to determine this in the other species). The area is 

 wanting in the females (Fig. 5) ; so is a secondary sexual character. 

 Moreover, the demarkation of the facets may appear in other species 

 which belong undoubtedly to the genus Syrphus. In 5". arcuatns 

 (Fallen), as I have discovered, this area is of sporadic occurrence, 

 in a few males (Fig. 3), while in a related species, 5". pcrplcxns 

 Osburn.f the line of demarkation is present to some degree in a 

 majority of the males (Fig. 4), though some do not have it. I have 



* Wien. ent. Zeit., Ill, 197. 



t Studies on Syrphidse, Pt. I, p. 55. 



