70 AMERICAN DIPTERA. 



pair; prescutellar a small pair; fronto-orbital only one, very small; 

 no sternopleural ; one pteropleural. 



Third joint of the antenna rounded, rather large, with long, bare 

 arista; face receding, oral margin but little prominent, about as in 

 Anorosto7na. 



Wing of ordinary Helomyzid form, costal spines distinct. 



The name is from Porsena, one of the invaders of Rome ; we 

 change the ending to avoid the confusion of a masculine noun with 

 a feminine ending. Accent on the first syllable. 



The singular chsetotaxy renders the species and genus easily 

 recognizable, as tiiere are half a dozen good generic characters. 

 The head of the single type was accidentally destroyed after it had 

 been drawn and some notes made, but a further examination in 

 regard to the fronto-orbital bristles and the form of the oral margin 

 would have given us a little greater certainty on these points. 



Porsemis johiiKOiii Darlington, n. sp. (PI. IV, fig. 2). 



Length, 4.7 mm. ; of wing, 5.7 mm. 



General color ashy gray, with yellow legs. 



Occiput gray; front brown; eyes rather large, round; orbits silvery ; cheeks 

 about three-fourths the width of the eyes, somewhat cream colored ; first two 

 joints of the antenna reddish, third cinereous, round, arista rather long, only 

 microscopically pubescent; one rather long vibrissa on each side. 



Dorsum of thorax gray, the lateral edges a little yellowish, median part with 

 coarse and rather dense hairs; mesopleura bare, except for two or three coarse 

 hairs on the front edge, just below the spiracle; sternopleura densely pubescent 

 all over, with no bristle; pteropleura with one good-sized bristle and several- 

 coarse hairs. 



Abdomen gray, the posterior margin of each segment somewhat reddish. 



Wings with a faint brownish tinge, hind cross-vein slightly infuscated. The 

 submarginal cell is rather noticeal)ly widened in front of the anterior cross-vein. 



Legs yellowish, with few bristles; femora indistinctly darker; tarsi moder- 

 ately infuscated. 



One female. Johnson : Boston, Mass., October I'Jth. 



ACH.KTOMIJS. 



Coquillett, Canad. Ent., xsxix, 75, March, 1907. 



"Near Hcfomyza, as restricted by Loew, but with only two pairs 

 of dorsocentral bristles, propleural present, two pairs of fronto- 

 orbitals, etc. Eyes circular, clieeks nearly as wide as the eye- 

 height, third joint of antennae broader than long, arista dorsal, bare. 

 Femora without bristles, tibite witli apical and preapical bristles 

 oidy. Venation as in Heloimjza, spines of co.<ta well-developed. 

 Type, the following species: 



