48 BULLETIN OP THE BUREAU OP FISHERIES. 



insufficient for a larger form with similar food requirements. It is this factor that seems 

 most readily to explain the wide range and great numerical dominance of the family. 

 It is this fact, too, which seems best to account for their numerous enemies among the 

 aquatic animals. 



ORPHNEPHILIDjE. 



This family is included here because of its close kinship with the Chironomidae, as 

 shown by the structure of the adult. It is also of considerable interest on account of 

 the unique and little known habits of the larva, which lives on the surface of ledges 

 covered by only a thin film of water (fig. 38) and breathes by means of a trachea, ren- 

 dering it entirely unable to live submerged for any considerable time. As might be 

 inferred from these two conditioning factors this family is not likely to occur in many 

 parts of the country. That it is really scarce is well illustrated by the fact that the 

 record for the family in this country prior to 1916, so far as known, was based on three 

 specimens found by Dr. O. A. Johannsen at Ithaca, N. Y. Dr. V. L. Kellogg (1902) 

 states that he has examined specimens of every family of the Nematocera except 

 Orphnephila. References in the literature to this family are so infrequent as to make it 

 almost unknown except to a specialist in Diptera. Thienemann (1909), however, 

 found and described the larva which he obtained from mountain streams in Europe. 

 His paper considers the nature of the habitat, the distribution, and the method of 

 locomotion of the larvae of Orphnephila testacea. According to Kellogg (1905, p. 327) 

 this species is the only one representing the family in this country and as far as the 

 author is aware the only species known, if the American and European forms are actu- 

 ally identical. 



The three adult flies found by Dr. Johannsen referred to above were taken in sweep- 

 ing for insects, and none were taken in a manner to reveal the whereabouts of their 

 immature stages. It was therefore a very pleasant surprise to the author to accidentally 

 run across the habitat of this most unique semiaquatic insect in the environment of 

 Ithaca, the only place in this country where this species is known to occur. 



As the interests of the author centered about the ecology of the species, especially 

 as it concerns the feeding habits of the larvae, he several times attempted to take speci- 

 mens into the laboratory that the necessary conditions of their environment might be 

 more readily studied. Several of these attempts were failures because the larvae were 

 drowned while en route, but by lining test tubes with moist cheesecloth it was found 

 very easy to carry any number of the larvae considerable distances under perfectly 

 normal conditions. 



HABITAT. 



While Thienemann's description is in substantial agreement with the writer's own 

 observations, it seems best to summarize the conditions under which the larvae were 

 found. 



The horizontal strata of the rock, so characteristic of all the gorges and "hanging 

 valleys" in the environment of Ithaca, together with the usually rather irregular ver- 

 tical cleavage, frequently gives rise to a stair-stepped bottom to the streams that enter 

 the deeper valleys. The only habitat in which these larvae were found was on a series 

 of "giant steps" (fig. 38), where a small stream spreads out over these broad and nearly 

 horizontal stones in its precipitous descent to the valley of Six Mile Creek. Here the 

 larvae were found rather more frequently on the vertical than the horizontal surfaces of 



