16 
BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 
have the antennse 4- jointed, the first long joint described by Johann- 
sen being divided by a very distinct suture. Though the first and 
second joints are very closely articulated and rigid, the constant 
occurrence of a distinct suture between them seems to indicate clearly 
the existence of two segments. The third segment is slender cylin- 
drical, and the fourth a short conical process. 
There are two conical processes situated at the apical end of the 
second segment, which seem to be sense organs. The antennae of S. 
vittatum (fig. 11) are 5-segmented, the second segment being again 
divided. The sense organs are borne on the apical end of the third 
segment. In color the antennae vary with 
the species from yellowish hyaline to dark 
brown. 
The mandibles are situated just below 
the fans and move horizontally. With 
the exception of a slight difference in size, 
according to the species, there are no con- 
stant characters of real systematic value 
in the mandibles. 
The following is a description of the 
mandibles of S. venustum: 
The mandibles (fig. 12) are very chitinous, 
stout, somewhat elongate, with the outer lateral 
margin rounded. There are from two to four 
large teeth at the apex on the inner lateral 
margin, almost dense black in color. Situated 
immediately dorsad along the inner margin of 
the largest tooth is a row of from six to eight 
smaller teeth of the same shape, but much 
lighter in color and gradually decreasing in size. 
Behind this row, on the ventral surface of the mandible, arising generally from 
the third or fourth tooth, is a second row of small, sharp-pointed teeth very pale 
in color, about 10 to 14 in number, which continues along the basal portion of 
the lateral margin of the largest apical tooth. Laterad of this second row of 
teeth, on the inner margin of the mandibles, there is a large wide-angled flat- 
tened tooth, very pale in color, followed by a smaller one of the same descrip- 
tion. Near the apex of the mandible, a short distance from the outer lateral 
margin of the ventral surface, are two large bristles arising from almost the 
same point. At the base of the large apical teeth, on the ventral surface, are 
two clumps of stout hairs. There is a fringe of long hairs on the dorsal sur- 
face of the mandible, which extends halfway down, commencing at the apex, 
where it almost obscures the apical teeth. Opposite the base of this fringe on 
the inner lateral margin of the mandible there is a fan of long hairs, and a 
fringe of very long hairs, which continues down to the base, gradually devel- 
oping into bristles explanate and divided at apex. 
The maxilla? are situated immediately ventrad and mesad of the 
mandibles. The maxillary palpus is short, cylindrical, and bears 
on its distal end several small cone-shaped protuberances similar to 
Fig. 12. — Simulium venustum. 
Left mandible of larva, ven- 
tral view. Greatly enlarged. 
(Original.) 
