with notice of a new Genus o/Diptera. 389 



its surface, and two long ones at the apex of the scutellum ; ab- 

 domen shining black, its hairs also black, the hinder edges of its 

 segments narrowly lighter or subcinereous ; a white band along 

 each side w hen alive ; beneath with a black, gradually widening 

 band down the belly, composed of a series of shining black spots 

 set in a whitish edging, the first square, the succeeding parallelo- 

 grammic, the last sinuated on the hinder edge, anal segment 

 black ; legs black, tip of the anterior thighs whitish, in the other 

 pairs less distinctly paler ; poisers white ; wings nearly hyaline, 

 with fine iridescent tints of purple, blue, green, orange and 

 brown ; their insertion whitish ; the costal cell has a cross nerve, 

 and is inclosed by two short curved nervures, the upper very 

 faint, the lower strong and black : there are five longitudinal 

 nervures, of which the two upper are strongest, and a faint sixth 

 or anal one that does not reach the lower edge of the wing ; the 

 third has a small cross nerve betwixt it and the second before the 

 junction of the latter with the first, and is united with the fourth 

 by a small transverse line near the base of the wing ; the fifth 

 springs from the root of the wing and unites with the sixth by 

 an arched cross line that runs to the short stronger one that 

 combines the third and fourth. Length f-1 line. Expansion of 

 the wings 2 lines. The female is the larger, and has the abdo- 

 men ovate and sharp at the tip ; that of the male is more cylindric, 

 with the apex obtuse. When dried the white lateral lines of the 

 abdomen are generally obliterated, and the belly and upper sur- 

 face become of a uniform black. The first of these flies appeared 

 on the 15th of August, the day on which I gathered the pupae; 

 others came out on the 27th, and again on September 3rd. The 

 earliest period at which I have taken them in the woods was in 

 the beginning of April, when they frequented the trunks of some 

 recently felled birch-trees to feast upon the sap. The larva is 

 infested by a small parasitic Ichneumon that attacks several other 

 species, and must considerably diminish their numbers; those 

 that become pupse late in the season being almost as likely to 

 produce parasites as flies. 



The fly belongs to the Acalypterate division of the Muscidse, 

 and owing to the comparative imperfection of its organization 

 is placed near the termination of the series. Its position in the 

 arrangement is with the Heteromyzid<e : in the present instance, 

 however, the nervures of the wings present an exceptional cha- 

 racter ; the mediastine nerve being double, and not simple, as it 

 is said to be in this family. The species appears to be the Phy- 

 tomyza nigra of Meigen, Europ. Zweif. Insekt. vi. 191, which 

 he designates briefly as " nigra ; thorace cinerascente ; halteribus 

 genubusque albis ; alis hyalinis.^' The only doubt as to this, 

 arises from another species occurring, which, as a fly, it is almost 



