TRANSFORMATIONS OF BUFFALO GNATS. 
17 
Fig. 13. 
-Simulium vittatum. 
Greatly enlarged. 
Labial plate of larva. 
(Original.) 
those borne on the third segment of the antenna. The lacinia bears 
mesad and cephalad fringes of long hairs and bristles. On its distal 
end there is a single spurlike process. 
The labrum is short, rounded, fringed with long hairs, and is situ- 
ated overhanging the hypopharynx. It is reinforced on its dorsal sur- 
face by a strong T-shaped 
sclerite. The apical mar- 
gin is sometimes serrate. 
The labium (figs. 4, 5, 
9, 13, 14), which almost 
covers the ventral surface 
of the hypopharynx, is 
composed of two or more 
broad chitinous united 
plates. It is immovable. 
The apical edge of the 
ventral plate is serrate. 
The lateral and apical margins of the dorsal plate are also serrate 
and the apical margin usually bears a very prominent central tooth. 
In some species the teeth are trifid, and in others simple. There 
is a row of from three to 10 long bristles near each lateral margin 
of the ventral plate. The number and shape of the teeth and the 
arrangement of the bristles are of systematic value in separating the 
different species, and Robaud and Malloch 1 consider these char- 
acters to be of possible 
generic value. There is 
a certain amount of in- 
dividual variation, but 
seemingly within defi- 
nite limitations. 
The dorsal portion of 
the head in most species 
has distinct markings 
of very characteristic 
arrangement. (PL IV, 
figs. 1-4.) Though sub- 
ject to a certain amount 
of individual variation, they are of systematic value in separating 
the different species especially when combined with other more con- 
stant specific characters. These markings are formed by a collection 
of large cuticular cells which, in some species, such as S. vittatum, are 
strongly pigmented, while in others, such as S. vemistum, they are 
normally almost devoid of pigment, the surrounding area being dark. 
Fig. 
14. — Simulium pictipes. 
Greatly enlarged. 
Labial plate of larva. 
(Original.) 
1 Malloch, J. R. American black flies or buffalo gnats. 
Tech. Ser. no. 26, 71 p. (p. 8), 6 pi., 1914. 
10981°— Bull. 329—16 3 
U. S. Dept. Agr. Bur. Ent. 
