. Bulletin of the Department of Agriculture. Agriculture; Agriculture. quire swiftly flowing water for their development. The full-grown larva of the largest species, according to Johannsen, measures not more than 15 mm. in length. The American species known to the writer measure from 12 mm. (S. pic- tipes) to mm. (S. jenningsi). The larvae are generally subcylindrical, somewhat attenuated at the middle, and with a gradual dilation toward the anal extremity. In addition to the head there are 12 rather indistinct body segments. In -the larval stage the shape and number of the branches
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. quire swiftly flowing water for their development. The full-grown larva of the largest species, according to Johannsen, measures not more than 15 mm. in length. The American species known to the writer measure from 12 mm. (S. pic- tipes) to mm. (S. jenningsi). The larvae are generally subcylindrical, somewhat attenuated at the middle, and with a gradual dilation toward the anal extremity. In addition to the head there are 12 rather indistinct body segments. In -the larval stage the shape and number of the branches of the rectal gills seem to be good sys- tematic characters, not differing essentially among individuals of the same species. If the number and length of the an- tennal joints, the teeth in the mentum, and the character of the dorsal markings fig. 3 of the head are also used, the de- termination of half-grown larvae is possible in their last stage can be corre- lated positively with their re- spective pupae by the dissection and study of the pupal filaments, which become fully developed under the larval skin. As the larvae of 8. bracteatum and S. jenningsi have not been pre- viously described, the follow- ing descriptions are given. DESCRIPTION OF LAEVA OF SIMULIUM BKACTEATUM. The full-grown larva is from 6 to mm. in length. The general color varies from light yellowish- brown to grayish, with conspicuous brownish markings on the ventral surface. The antennse (fig. 3) are slender, 4-segmentecl;* the second segment one and one-half times as long as the first; the third segment as long as the first; the fourth a short conical process; the general color pale hyaline; the first segment infuscate. The labial plate (fig. 4) is more strongly serrate than that of S. rcmistum (fig. 5) : the apical margin rather convex; the middle tooth and each corner tooth very large. There are from four to five long bristles near the lateral mar- gin on each side. Fig. 4.—Simulium bracteatum. la
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