1921} Metcalf: Genitalia of Male Syrphide 191 
STyLEs (mesostyli, Berlese; appendage I, Newell; claws, Lundbeck:; 
forceps inferiores, Wesche). The largest paired appendages of the 
postabdomen, with rare exceptions, are the styles. They are the 
appendages of the tenth segment (Fig. O, Plate IX), and stand more 
or less parallel to each other at the caudo-lateral corners of this segment. 
They articulate at base, typically broadly, to the tergite on the caudo- 
lateral margin and to the sternite on the cephalo-mesal margin; often 
the points of articulation are much restricted by emarginations of the 
tergite or the attenuation of the arms of the sternite. 
The shape of the styles varies endlessly in the different genera and 
species. They usually afford a generic character and also frequently 
valuable specific characters. Typically they are erect, somewhat 
compressed and more or less adapted to clasp together, forceps-like. 
Such a simple condition is found in species of Chrysotoxum (Fig. 59, 
Plate XIII), Syrphus (Figs. 55, 56, Plate XIII), and Mesogramma 
(Figs. 43, 46, Plate XIII). Even in the most primitive-that I find, 
there is a strong tendency toward the excavation of the mesal face, 
while the lateral surface is generally convex. From this medium con- 
dition there are several lines of departure. In one of them the style is 
progressively longer and more nearly cylindrical. Note Paragus 
guadrifasciatus (Figs. 9 and 10, Plate X), species of Pipiza (Figs. 12, to 
26, Plate XI), Chilosta (Figs. 27 to 29. Plate XII), Chrysogaster (Figs. 
36 to 41, Plate X), Sphegina (Figs 73, 74, Plate XIV), Syritia and 
Eupeodes (Fig. 134, Plate XIX). Almost invariably accompanying 
this elongation is a greater distortion evidenced by sharp curving mesad 
abapes (ries. 12, 14. 17, 20, 21, Plate XI; 50, Plate XIII; 73, Plate 
XIV; 108, Plate XVII; 133, Plate XIX); by a curve near the base 
(Fig. 18, Plate XI; 40, 42, Plate X; 72, Plate XIV); or by curious 
bends and twistings somewhere about mid-length (Note Figures 2, 
Plate XV; 41, Plate X; 71, 79, Plate XIV, and 134, Plate XIX). The 
vestiture is almost always longer on the lateral surface and very often 
short and stiff or peg-like on the surfaces which are brought to contact 
when clasping, i. e., usually toward the apex on the mesal face. The 
apex also frequently becomes capitate, or serrate, or spurred or claw- 
like (Note Figures 24, Plate XI; 36, Plate X; 69, Plate XIV; 108, 109, 
Plate XVII: 134, Plate XIX). 
A second line of departure from the typical, erect, compressed 
style is toward a greater broadening out cephalo-caudad to make an 
erect, short, thin style very wide cephalo-caudad. This is particularly 
characteristic of the genus Sphaerophoria, (Note Figures 1, 60, 66, 
Plate XV). 
A third line of specialization 1s shown by many genera in the tendency 
to become forked or biramous or to develop an accessory lobe in addition 
to the principal one. This takes many forms and may be associated 
with either of the above types of style, i. e., with a long slender or a 
short broad one. This bilobed condition is very pronounced in 
Sphaerophoria spp., in which the lobes may be about equal in size 
(Fig. 66, Plate XV) or the caudal one much larger (Figs. 63 and 64) 
or the cephalic one larger (Fig. 60). Small lobes of various kinds 
