2S2 DIPTERA OF NORTH AMERICA. [PART IV, 



long as the head and thorax taken together, the flagellum with 

 nearly cylindrical, elongated, densely-pubescent joints, of nearly 

 equal length, except the last, which is shorter. The knob of the 

 halteres is distinctly iufuscated ; the stigma, likewise, is slightly 

 brownish; the vertex seems to be darker than in D. rivularis ; 

 the wings of the male are somewhat narrower, and the prrefurca 

 a little longer; the interval between its origin and the nearest 

 marginal cross-vein, in both specimens which I have before me, 

 is longer than the interval between the two cross-veins. 



I have two males iu ray possession, taken together with the 

 specimens of D. rivularis. At that time (compare Proc. Acad. 

 Nat. Sci. Philad. 1859, p. 250) I was uncertain whether they did 

 not belong to the latter species. I venture now to describe them 

 as distinct ; the antennaB are of a length which is otherwise un- 

 usual in the genus. 



Gen. XXXIX. PLECTROMY5A. 



Two submarginal cells ; four poftterior cells ; discal cell open ; the sub- 

 costal cross-vein is a considerable distance before the origin of the second 

 longitudinal vein ; the marginal cross-vein is very near the tip of the first 

 longitudinal vein (Tab. II, fig. 18). Tibiffi with exceedingly minute spurs 

 at the tip ; empodia small, but distinct. Eyes pubescent ; antennae 13- 

 jointed. The upper horny appendage of the forceps of the male is Hat, 

 rounded, with a serrate edge. 



A rather broad front separates the eyes above ; in well pre- 

 served dry specimens, it rises abruptly above the antenujB and is 

 rather convex, without showing any trace of a bump (having 

 neglected to describe it from a fresh specimen, I have abstained 

 from any statement about it in the generic character). Rostrum 

 short ; palpi short ; the first joint is the longest, the others stout, 

 short; the last is not much longer than it is broad. Antennae 

 13-jointed (I have counted the joints on fresh specimens) ; first 

 joint elongated, subcylindrical ; the joints of the flagellum, except 

 the first, which is subconical, are rounded, slightly elongated, 

 with short verticils ; they are clothed with a short pubescence, 

 which is more dense in the male ; if bent Jiackwards, the antennae 

 would not reach the root of the wings. Collare well developer', 

 with a short, neck-like pi'olongation towards the head ; the meta- 

 notum moderately gibbose above it ; thoracic suture w^ell marked. 

 The feet are long (although much shorter than in Rhaphidolabis) ; 



