36 BULLETIN OF THE BUREAU OF FISHERIES. 



minutes while creeping over moist stones seems to be an adaptive measure. The upper 

 portion of the body would become dry and the surface film would break away from the 

 larva if it were not for the frequent moistening of the entire surface of the body. This 

 revolving of the body about on its long axis the larva accomplishes by bending its head 

 and the first two or three segments of its body off to one side, then, by relaxing the 

 underneath muscles and stressing the upper muscles, this angle is made to revolve about 

 the body until the larva again reaches an upright position. 



These larvae feed upon the organic debris to be found on the ledges in flowing water. 

 Those whose stomach contents were studied had eaten Cladophora almost exclusively, 

 and both the cell contents and the cell walls could be recognized. There were also a few 

 diatoms, several filaments of Oscillatoria, and a few spherical cells, possibly of Aphano- 

 capsa sp. The well-developed silk glands are doubtless used by the larvae as digestive 

 glands, and their development may be due to the coarse organic nature of their food. 



Group VI: Subgroup C. — Prodiamesa sp. 



The genus Prodiamesa was established by Kieffer in 1906. In the "Genera 

 Insectorum" he refers six European species to this genus, and the writer has found 

 only one South American species which has subsequently been referred to it. There 

 is therefore no record of the occurrence of the species of this genus in this country. 

 The species upon which these observations are based has been bred, and, from the 

 larval mouth parts figured by Kieffer and Thienemann (1908), it is found to resemble 

 Prodiamesa prcecox very closely. The adult description, however, does not agree with 

 that of P. prcecox, and it seems probable that it will be found to be a new species. 



The larvae are yellowish white with reddish-brown heads and brownish claws on 

 the prolegs. They, as well as the larvae of the genus Diamesa, are characteristically 

 found in flowing streams. The larvae of Prodiamesa were found burrowing through 

 the coarse debris that had accumulated in a roadside watering trough which was fed 

 by a rapidly flowing stream from a near-by hillside. The trough was nearly full of 

 sticks, grass, and leaf mold in various stages of decay, and it was through this rather 

 loosely aggregated material that the larvae were seeking their food. 



BODY STRUCTURES. 



This genus as represented by the writer's material (which is essentially in agree- 

 ment with the larva of Prodiamesa prcecox) is structurally quite similar to the burrowing 

 forms. This is especially true of the anterior prolegs which are made up of several 

 rows of fine spines. The branchial gills of the eleventh segment are absent in this 

 genus. The caudal filaments are well developed. 



MOUTH PARTS. 



The most characteristic modifications in the mouth parts are to be observed in 

 connection with the maxilla, the hypopharynx, and another structure the homology 

 of which has not yet been satisfactorily established. 



The maxilla is capable of a great deal of free movement, as the basal portion (as in 

 the other species in this group) is not fused to the adjacent epicranial plate (fig. 31). 

 Its inner mesad projecting process (fig. 31, t) is provided with numerous fingerlike 



