Localities in which Pellagra is Prevalent. 13 



The insect has doubtless become less common than it 

 was formerly, yet my brief stay in the mountains was 

 sufficient to show that it is still there and probably more 

 abundant than is commonly supposed. My own material 

 is all immature, yet the characters of the pupse and larvae 

 are such as to leave little doubt as to the correctness of their 

 identification. The following detailed descriptions are based 

 upon the material collected at Gary and PineviPe, and 

 together with the illustrations made by Mr. Matthews of 

 the Division will serve for the recognition of the insects, 

 should any one wish to search for them in the streams. 



Fig. I— Larva of Sitniilium venustum from the Left 

 F-rk o( Straight Creek, Ky., 1911. 



Larva. —Rather thick bodied, more slender at the mid- 

 dle, becoming greatly thickened at the posterior extremity, 

 and enlarging somewhat behind the head. Head relatively 

 large, brownish, bearing two large brushes of long curved 

 bristles. A false leg, bearing rust-brown chitinous hooks at 

 the tip, arises from the first body division and projects for- 

 ward beneath the head. Posterior extremity with a ring of 

 dusky microscopic hooks by which the insect secures itself 

 to rocks and other objects. Translucent white, with black- 

 ish markings, in the larger examples sometimes assuming 

 the form of cross bands. Length of largest example se- 

 cured, 4 millimeters or about 0.16 inch; diameter of swollen 

 posterior region about 0.6 mm. Collected, first, September 

 1, 1911, in a rapid of the Left Fork of Straight Creek, a few 

 hundred feet from a dwelHng in which were four cases of 

 pellagra. Later, collected in Cumberland River, near Pine- 

 ville. and at different points in Straight Creek. 

 Head large, its depth three-fourths its length. The fans 



