THE CANADIAN ENTOMOLOGIST 311 



Type in collection of Illinois Natural History Survey, para- 

 types in collection of U. S. Bureau of Biological Survey. 



TWO NEW HYDROT^AS. (DIPTERA, ANTHOMYID^). 



BY J. M. ALDRICH, 



Bureau of Entomology, U. S. Dept. of Agriculture 

 The two species herein described possess the common charac- 

 ters of the genus,^ — sixth vein not reaching the margin of the wing, 

 scutellum bare below, hind calypter projecting beyond the front 

 one, four posterior dorsocentrals, and in the male two teeth on 

 the underside of the front femur near tip. Males of the genus are 

 quite easily separated by the armature of the legs, but these 

 characters are greatly reduced or mostly absent in females, which 

 are in several instances very difficult to distinguish. Mr. Malloch 

 has tabulated the males for the known North American species in 

 Bulletin of the Brooklyn Entomological Society, XI, 108, 1916, 

 and the females in the same journal, XIII, 30, 1918. With the 

 two herein described we have a total of 17 species, of which 9 are 

 European. 



The function of the femoral teeth which occur regularly in 

 the males has not been observed to my knowledge. I surmise 

 that the male grasps the front edge of the wing of the female with 

 the femur and tibia during copulation; while this is merely a 

 theory, it is offered as a stimulus to observation. 



Hydrotaea orbitalis, n. sp. 



Male. — General colour deep black, only the abdomen notice- 

 ably poUinose. Eyes bare, separated on the front by about two- 

 thirds of the space between the hind ocelli, the black median stripe 

 distinct to ocelli, orbits very narrow, widening close to the antennae, 

 shining black to the level of the arista, below this like the flat 

 facialia they are thinly brown pollinose; lunule white pollinose; 

 antennae black, of ordinary size, arista bare; palpi and proboscis 

 black. Thorax subshining black above, more opaque black 

 anteriorly, with no stripes; pleurae wholly shining except a space 

 above hind coxae, which with the postnotum is thinly brown 

 pollinose. Prealar wanting; two or three pairs of anterior acrosti- 

 chals in rows close together, a few verv delicate hairs barely visible 



September, 1918 



