with notice of a new Genus of 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 when 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 3-1 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 pupe; 
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 Jehneumon that attacks several other 
species, and must considerably diminish their numbers; those 
that become pupz late in the season being almost as likely to 
produce parasites as flies. 
The fly belongs to the Acalypterate division of the Muscide, 
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 Heteromyzide : 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 im 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 
