388 Annals Entomological Society of America [Vol. VI, 



are typical of this generalized condition. On the concave 

 inner surface of the labrum are two patches of incurving hairs, 

 and these are supplemented by a set of long marginal hairs. 

 When gathering food the edge of the labrum is pressed against 

 a stem or leaf and moved rapidly back and forth. After a few 

 movements its tip is pulled close to the mouth and brushed 

 by the maxillary palpi. The labium sweeps food in from behind 

 as the labrum does trom the front. On the maxillae which lie 

 in front of the labium the lacinia and galea are fused. The 

 lacinia is represented by two teeth on the tip; the galea by the 

 lobe like part behind them. The teeth of mandibles are 

 separated into two distinct groups, the canines (c) and the 

 molars (m). In many cases both of these are very asym- 

 metrical. Both maxillag and mandibles may be freely ex- 

 tended side wise, but the latter is used less often for biting than 

 for grinding. The epipharynx (cf. PI. XLVII, Fig. 14b) is an 

 inconspicuous elevation which is borne on the inner surface 

 of the labrum. It is densely covered by short incurved hairs 

 probably sensory. It often extends on to the clypeus and in all 

 the nymphs examined lies a little to the right of the center. 

 Mouth-parts of the type described above are found in nymphs 

 of Siphlurus, Blasturus, Baetis and Leptophlebia. The food 

 getting habits of any of these can be easily observed. They 

 pull off fragments from the stems and leaves by sticking the 

 laciniae or less often the canines into the tissue, then bracing with 

 the front feet and pulling backward. Upon flat surfaces, they 

 keep the labrum and labium moving rapidly and thus sweep 

 the food into the mouth. 



In nymphs of Ameletus ludens a broad plankton rake upon 

 the maxillae formed by a series of arched, regularly grad- 

 uated, and pectinated hooks borne upon the distal end of 

 the galea and lacinia. When eating, the nymph extends 

 these rakes forward and backward, exactly as one would 

 use a hand rake and by the help of the labium and hypopharynx 

 the food is pulled into the mouth for grinding. 



Nymphs of Chirotonetes gather their food upon ledges 

 washed by dashing water. The outer surfaces of the mouth 

 parts are armed with very long bristles. The distal segment 

 of the labial and maxillary palpi are flattened out into broad 

 blades. These blades are used as scrapers upon the algae cov- 

 ered stones. In the swift current this nymph must of necessity 



