1921] Metcalf: Genitalia of Male Syrphide 201 
Both pairs are present in Hammerschmidtia ferruginea, Brachyopa 
notata, Chilosia spp., (Figs. 27, 30. Plate XII) Rhingia nasica (Fig. 32, 
Plate XII). In Microdon and Mixogaster, there are neither inferior nor 
superior lobes (Figs. 129, 130 and 133, Plate XIX). 
(k). Tue SupERIoR Loses are usually larger than the inferior ones 
and when only one pair is present it is usually clearly the inferior lobes 
which are wanting. In Chilosia, however, the superior lobes are regularly 
smaller (Figs. 27 to 30, Plate XII). Like the styles these lobes are subject 
to the greatest modification of shape, size and vestiture. There appears 
to be considerable correlation between their development and the 
simplicity of the styles: that is, the more complicated and efficient the 
styles the less developed are the penis lobes (note Calliprobola, S phero- 
phoria, Eupeodes, Sphegina, Xylota, Criorhina); and when the styles are 
simple the penis lobes are often highly developed (e. g., Chilosia, Paragus, 
Rhingia). Their more typical form appears to be a compressed, ovate, 
erect lobe, standing parallel to the sagittal plane and attenuated some- 
what distad, (Note Figs. 19, 25, Plate XI; 46, 49, 50, Plate XIII). 
But from this shape we find the greatest variation, which can best be 
appreciated by a reference to the accompanying figures. Frequently 
they are more cylindrical and erect (Figs. 4, Plate XV; 34, Plate SLL: 
and 87, Plate XVI) and may be enlarged distad (Figs. 36 and 37e, 
Plate X) or much pointed distad (Fig. 118, Plate XVIII) or incurved 
toward each other (Fig. 83, Plate XVI) enhancing their prehensile 
value; sometimes with serrations, (Fig. 40, Plate X). Frequently these 
serrations take the form of a definite ctenidium as shown in Figures 
30, 32, Plate XII; 91, 93, Plate XVI;. 107, 123, Plate XVII; .111 to 
113, Plate XVIII. Many species have poorly differentiated, shapeless 
or irregular superior lobes very difficult to describe (Note Figures 96, 
100, Plate XIX: 102; 104, 127;"Plate XVII;,-115, 118, Plate x WALL 
86, 89, Plate XVI). They are not infrequently bare but often have 
developed hairs, bristles, spines, serrations, claws or lamellae. They are 
peculiarly drooping behind the penis in Paragus (Figs. 6, 9, Plate X) 
and in Spherophoria (Figs. 1, 60, 63, Plate XV). 
(1). THe Iyrerior Loses arise at the cephalo-lateral corners of the 
apex of the penis-sheath. They are generally smaller than the superior 
lobes. They appear to be best developed in Paragus, (Figs. 5, 6, 11, 
Plate X), Chrysogaster, (Figs. 36 to 39), Chilosia (Figs. 27 to 30, 
Plate XII), and Pipiza, (Figs. 18, 19, 21, 23, 25, 26, Plate XI), and 
Blera (Figs. 115, 117, Plate XVIII). They are often more or less horn- 
like, though not infrequently simple lamelle-like projections of the 
corners of the penis-sheath. 
ASYMMETRY. 
Typically, the asymmetry in this family is very strictly confined to 
the last segment of the preabdomen and the segments of the post- 
abdomen, cephalad of the tenth. But in many species this tendency 
has spread also to the tenth urite and to the genital appendages. When 
unsymmetrical it is almost always the left side or the left appendage 
