THE CANADIAN ENTOMOLOGIST. S9 



The occurrence of the first discovered specimen of this European 

 genus in the western part of North America was another verification of 

 the well-known biological law that European forms are more likely to 

 occur in the western than in the eastern part of this Continent, as pointed 

 out by Snow. It is clear now, however, that since two species have been 

 discovered, one eastern and the other western, and the eastern as closely 

 related to the typical European forms as the western, that any such 

 conclusion in regard to this genus is no longer valid. 

 Microdon fu/gens, Wied. 



This species was included in Williston's Synopsis of N. A. Syrphidfe, 

 on the authority of Wiedemann, who described the species, Aussereu- 

 ropa^ischen Zweifl., Insecten 82 (I.), from a specimen " In Berliner 

 Museum, aus Neugeorgian," and on Macquart's statement. Dipt. Exot. 

 ler. Suppl., 122, of habitat as Florida and Guiana. Wiedemann's short, 

 terse description is abundantly sufiicient to separate it from its congeners. 

 It is as follows : — 



"Antennae black. Face steel-blue, thinly yellowish-white pilose. 

 Thorax golden-green ; in certain reflections there appear copper-coloured 

 stripes. Ante-alar callosities (Vorfliigeldreieck) steel-blue; front 

 between green and blue-metallic. Wings nearly pure brown, on the thin 

 veins only brownish ; tegulfe white with a black ciliate border. Legs 

 green or blue " [translation by Williston]. 



The front is mixed white and black pilose, front and middle tarsi 

 opaque black, pulvilli light yellow. Scutellum very broad, the posterior 

 margin almost parallel with the anterior; the spines distinct. The outer 

 cross-veins are distinctly sinuate. 



One specimen, a female [St. Augustine, Florida; Prof. C. W. John- 

 son], now in the collection of the University. 



The robust form, entirely metallic colour, black antennsa, and large 

 size are such as to make the species unmistakable. 

 CJirysotoxum derivatum, Walker. 



This genus is a very difficult one, and much confusion prevails even 

 in Europe as to the limitation of the species. Even such structural 

 characters as the comparative length of the antennal joints are of very 

 little value, although such an authority as Schiner has used them. They 

 all show a very great resemblance in coloration, and the species are 

 very variable. In Europe there are about fifteen described species, and 

 in this country ten, one of which must be dropped on account of the 

 imperfect description. 



