GUESTS AND PARASITES OF HALICTUS. 1 7 



immature condition. They were taken on the sand in the midst 

 of a colony of Halictiis. 



This species can readily be recognized in the male sex by the 

 enlarged third joint of the antenna. The female is not so charac- 

 teristic, but can be distinguished by the combination of structural 

 characters given in the description. It resembles most closely 

 P. ogarici Lintner, but has very short costal bristles. 



Stethopathus Wand. 



Among the insects frequenting the ground immediately about 

 the HalictHS-hurrows was one extremely small form, which from 

 its quick motions we immediately suspected to be a wingless 

 phorid fly. Such it indeed proved to be, but of quite a different 

 sort from any of our previously discovered North American 

 species. Its occurrence in New England is quite unexpected and 

 considerably extends the range of such forms, as none have 

 hitherto been seen in America north of central Texas. 



Its associations with the Halictus may be doubtful, although 

 no specimens could be found elsewhere whereas three females 

 were captured where the burrows of the bees were abundant. 

 Nests of Lasius iiiger and of Steiiamvia fulviim, variety piceiivi 

 also abound in such locations, but close scrutiny of the ant nests 

 revealed no specimens of the Phoridje. The fact that species of 

 PJiora occur as parasites of these bees would make it seem not 

 improbable that the Stethopathus has similar habits. We have 

 also a single winged male phorid, captured at the same time, but 

 which is probably the male of some other undescribed form on 

 account of its larger size and the different chaetotaxy of the head. 

 The description of this interesting little wingless fly, one of the 

 smallest known of all the Diptera, is given herewith. 



Stethopathus occidentalis sp. nov. 



Female. — Head rounded triangular, much rounded on the sides and at 

 the hind angles and obtusely pointed in front, about two thirds as long as 

 wide above, vertex descending rather steeply and evenly. Eyes small, 

 about one and one third times as large as the second antennal joint, 

 coarsely facetted with hemispherical ommatidiaas usual. Antennae placed 

 at the bottom of the deep frontal cavities. Proboscis long and stout, 

 equal to the head-height ; palpi small and slender, thickest near the tips, 

 with stout macrochsetas on the inner side. Ocelli present, placed in a small 



