TRANSFORMATIONS OF BUFFALO GNATS. 



17 



Fig. 13. — Simulium vittatum. Labial plate of larva.. 

 Greatly enlarged. (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 E-obaud 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. (PI. IV. 

 figs. 1^.) 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 JS. vittatum, are 

 strongly pigmented, while in others, such as 8. venustum, they are 

 normally almost devoid of pigment, the surrounding area being dark. 



1 Malloch, J. R. American black flies or buffalo gnats. U. S. Dept. Agr. Bur. Ent. 

 Tech. Ser. no. 26, 71 p. (p. 8), 6 pi., 1914. 



10981°— Bull. 329—16 3 



Fig. 14. — Simulium pictipes. 

 Greatly enlarged. 



Labial plate of larva. 

 (Original.) 



