70 ACADEMY OF NATURAL SCIENCES 



the disk, that in other species connects the inner branches of the 

 two bifurcated nervures together, is entirely wanting. 



Length one-fifth of an inch. 



[Wiedemann who had specimens communicated by Say before 

 him, describes this species as Dtloj)Jnis orhatus Say. I collected 

 a Dilophus in Florida which agrees very well with both descrip- 

 tions. The absence of the central cross nervure is not a constant 

 character ; although it is not seen in many specimens, some show 

 the cross nervure distinctly, others have it very faint, and others 

 again show a beginning of it. This cross nervure, when ap- 

 parent, is situated about half way between the upper cross ner- 

 vure and the fork. Wiedemann describes the female ; the sex is 

 not mentioned by Say, but he evidently refers to the same sex. 

 As I have several males in my possession, and they differ con- 

 siderably from the female, I take occasion to give the descrip- 

 tion. 



D. ORBATUS. % — Black, shining: feet black, with black hairs- 

 Wings pale yellowish, tinged with pale brownish along the ante- 

 rior border ; stigma fuscous ; nervures near the anterior border 

 brown ; the others very pale ; central cross nervure sometimes 

 wanting, sometimes distinct, and then situated as in the female. 



The color of the hairs on the feet, and the position of the 

 cross nervure distinguish the male of this species from the male 

 of another American Dilophus, {D. serraticollis Walker ?), which 

 is, besides, a little smaller. The females of the two species are 

 entirely diflFerent, and cannot be easily mistaken. — Sacken.] 



SCIARA Meig. Wied. 



S. FEMORATA. — Black ; thighs pale. 



Inhabits Pennsylvania. 



Wings hyaline, nervures fuscous; poisers large; coxae and 

 thighs pale, or yellowish-white; abdomen dirty yellowish obscure, 

 lateral margin and posterior margins of the segments blackish. 



Length less than one-tenth of an inch. 



DILOPHUS Meig. Wied. 

 1. D. STIOMATERUS.— Black ; stethidium and thighs rufous ; 

 two series of spines on the thorax, wings whitish with a dusky 

 costal spot. [ 79 ] 



[Vol. III. 



