PROCEEDINGS OF THE NATIONAL MUSEUM vol.69 



F^ Head broadly elliptical; arista as long or longer than 

 width of face ; metathoracic spiracle as large or larger 

 than third antennal joint; hind femur without spur 

 and usually slender (type X. segnis (Linnaeus)) 



Xylota. 



D^ " Bumble-bee flies " with dense yellow pile on anterior half and 



black pile on posterior half of mesonotum. 



E\ First posterior cell closed some distance before wing margin, 



a distinct petiole beyond ; metasternum fully developed 



Hadromyia. 



El First posterior cell closed practically at wing margin ; 



metasternal sclerites much narrower than long Pocota. 



Genus TEUCHOCNEMIS Osten Sacken 



TEUCHOCNEMIS BACUNTIUS Walker 



Usually a more robust species than lituratus^ thorax and abdomen 

 rather heavily marked with reddish brown. A rather rare species 

 found in the early spring. New Jersey, Maryland, Virginia, North 

 Carolina, Georgia, Texas. 



Type. — In Museum Comparative Zoology, Cambridge, Mass. 



TEUCHOCNEMIS LITURATUS Loew 



Differs from hacuntius by its entirely bluish-black abdomen. 

 Fairly common throughout northeastern America. Not reported 

 south of Virginia. 



Type. — In Museum Comparative Zoology, Cambridge, Mass. 



Genus PTERALLASTES Loew 



Four North American species have been assigned to this genus, 

 but from the present study it is evident that it should be restricted 

 to the original species, thoracius Loew. The other species, curvipes 

 Wiedemann {Polydontomyia) , perfldiosus Hunter and horealis Cole 

 belong to the tribe Helophilini, subfamily Eristalinae and not to the 

 Xylotinae. Characters which these three non-Pterallastes species 

 possess which ally them to Helophilini are: Face pilose, in profile 

 concave below the antennae, raised to an inconspicuous tubercle and 

 thence straight and slightly receding to the epistoma; third vein 

 deeply bent; hind femora greatly thickened, hind tibia arcuate. 



P. perfldiosus and horealis were described from females only. No 

 material is at hand for either species. They may prove to be con- 

 specific with certain species of Helophilus., and if horealis proves to 

 belong to the genus Hdophilus the name would have to be changed 

 as horealis is preoccupied in that genus. 



Other characters which ally P olydontoinyia curvipes to the Helo- 

 philini and which may be shared by per-fidiosus and horealis are: 

 Males broadly dichoptic ; front of female unusually broad and ocelli 



