Bui. 329, U. S. Dept. of Agriculture. 
Plate IV. 
Heads and Rectal Gills of Simulium Larv/e. 
Fig. 1. — Head of larva of Simulium pictipes. Fig. 2. — Head of larva of Simulium vittatum. 
Fig. 3. — Head of larva of Simulium jcvningsi. Fig. 4. — Head of larva of Simulium venus- 
tum. Fig. 5. — Rectal gills of larva of Simulium jenningsi, typical form. Fig. 6.— Rectal 
gills of larva of Simulium vittatum, variety with small lobes at base. Fig. 7. — Rectal 
gills of larva of Simulium bracteatum, typical form. Fig. 8. — Rectal gills of larva of 
Simulium pictipes, typical form. Fig. 9. — Rectal gills of larva of Simulium venustum, 
typical form. All greatly enlarged. (Original.) 
