1921] Metcalf: Genitalia of Male Syrphide 187 
In the following genera the tergites of the sixth, seventh and eighth 
urites are apparently not at all chitinized, the area occupied by these 
sclerites being thin and membranous: Paragus, Syrphus (pars), Xan- 
thogramma, Spherophoria, Allograpta, Eupeodes, Platychirus. 
(3) The third specialization of the postabdomen that tends to 
make interpretation difficult is the tendency for certain segments to 
fuse. The fusion of segment eight with nine is shown in the genus 
Paragus. In this genus there are five tergites in the preabdomen while 
the sternite of five has been transformed. In P. tibialis the postabdomen 
shows five distinct segments of which three (6, 7 and 8) are small, con- 
fined to the left side, and subequal. In all the other species examined, 
however, one can find only four segments in the postabdomen, there 
being only two smal] subequal urites on the left side between the fourth 
sternite and the large penultimate segment (nine). However when one 
clears the specimens and examines this ninth segment carefully an 
obscure suture becomes evident which is undoutbedly a line of fusion 
between segments eight and nine. The cephalic portion so marked off 
is of the right size and shape for the eighth segment and the caudal 
portion of this compound segment about equals in size segment nine of 
tibialis. 
Another example of the fusion of segment eight to nine is furnished 
by the species, Eupeodes volucris. (Fig. 134, Plate XIX). In. this 
species a triangular eighth segment is fused to the left basal corner of 
the enormous ninth. The suture in this case is distinct toward the 
lateral margin but has wholly disappeared toward the median line. 
Urite NINE appears to consist of a single sclerite; and in the 
absence of any spiracles on this segment it is a little puzzling to know 
whether it is sternite or tergite. Its relation to sternites eight and 
seven (Figs. B, D, K, L, N) makes it seem almost certainly a sternite; 
while the interpretation we have made of the tenth urite (calling the 
larger more convex sclerite the tergite) and the position of the penis 
(which we consider the appendage of urite nine) makes it seem equally 
certain that it is the tergite of nine that is represented. Most likely 
it is a fusion of both sclerites, completing the tendency cited above for 
these sclerites to fuse on the left side. In the absence of proof on this 
point we shall call the sclerite write nine. This urite may extend farther 
basad on the right (Figs. A, B) or on the left or about equally on both 
(Figs. E, G, F, H), depending on the relative size of segments eight and 
ten. It is almost always larger than the preceding segments of the 
postabdomen and very frequently also much larger than the succeeding 
ones. It is very convex, the entire convexity forming about half a 
spheroid against the median diameter of which rests the base of the 
penis (Fig. O). 
In the description of the segments of the postabdomen and of their 
appendages the peculiar flexure is of course kept in mind and the cardinal 
directions, aspects and margins are described as they would appear if 
the abdomen were in the normal position. 
