18 PBOCEEDINGS OF THE NATIONAL MUSEUM. tol. 60. 



BIBIO THORACICA S«y. 



Bibio thoracica Say (Thomas), (in Narrative of an Expedition to the Source 

 of St. Peter's River, etc., under the Command of Stephen H. Long, vol. 2. 

 1824, p. 368), Gompl. Writings, vol. 1, 1859, p. 250. [East Florida.] 



Genus DILOPHUS Meigen. 



SET TO THB SPECIES : MALSS. 



A. Front tibia with three series of spines 1 spinipea. 



AA. Front tibia with two series of spines. 



B. Wings dusky to black throughout serotinus. 



BB. Wings chiefly hyaline, 



C. Rostrum " nearly or quite as long as antenna stigmaterus. 



CO. Rostrum distinctly shorter than antenna. 



D. Genital segment cleft half or less than half its length. 



E. Genital segment cleft distinctly less than half its length. 



F. Length of wing, 5-6 mm. ; stigma faint tibialis. 



FF. Length of wing, 4 mm. or less; stigma distinct strigilatus. 



EE. Genital segment cleft about half its length. 



G. Body and legs with dark hair orbatus. 



GG. Body and legs with pale hair. 



H. Hind margin of superior genital plate straight or nearly so. 



I. Superior plate about as lang on median line as across straight 

 part of bind margin breviceps. 



II. Superior plate more transverse, about four times as wide as 

 long proximus. 



HH. Hind margin of superior genital plate obviously concave or 

 emarginate. 

 J. Superior plate gently to decidedly concave. 



K. Superior plate, less transverse, about three times as wide as 



long caurinus. 



KK. Sui)erior plate more transverse, about four times as wide 



as long obesulus. 



JJ. Superior plate conspicuously angulate emarginate. 



emarginatus. 

 DD. Genital segment cleft nearly to base sectus. 



K2Y TO THE SPECIES : rEMALBS. 



A. Front tibia with three series of spines spinipes. 



AA. Front tibia with two series of spines. 

 B. Wings dark. 



C. Thorax, coxae, and femora rufous serotinus. 



CC. Thorax black, legs brown to black orbatus. 



BB. Wings chiefly hyaline. 



D. Rostrum nearly as long as antenna stigmaterus. 



DD. Rostrum distinctly shorter than antenna. 



E. Thorax chiefly rufous above. 



F. Prothoracic comb very prominent, nearly equaling eye in height. 



strigilatus. 



FF. Prothoracic comb much lower breviceps. 



EE. Only the humeri (of upper surface of thorax) rufous. 



G. Mid and hind femora dark emarginatus, 



GG. All femora pale. 



H. Mid and hind tibiae and tarsi dark. 



obesulus; sectus; tibialis; caurinus, 

 HH. Mid and hind tibiae and tarsi pale proximus, 



» This term refers to the chlttDized portion of head below eyes, not to the prohoscis, 

 which is more or less ertensible in all species. 



