. 14 DIPTEKA OP NORTH AMERICA. [PART II. 



SYSTEMATIC ARRANGEMENT OF THE GENERA. 



I. First joint of the antennae with hairs on its upper side. 



A. Hypopygium disengaged. 



A. Palpi of the male small. 



1. First joint of the hind tarsi bristly. 



Gen. I. Hygroceleuthus. Gen. II. Dolicliopus. 



2. First joint of the hind tarsi not bristly. 



a. Third and fourth longitudinal veins parallel or sub- 

 parallel. 



Gen. III. Gynmoptermis. 



6. Third and fourth longitudinal veins convergent. 



Gen. IV. Paraclius. Gen. VIII. SyMstroma. 



Gen. V. Pelastoneurus. Gen. IX. Hercostomus. 



Gen. VI. Tachytreclms. Gen. X. Hypophyllus. 



Gen. VII. Ortliocliile. Gen. XL Haltericerus. 



B. Palpi of the male conspicuously large. 

 Gen. XII. Diostracus. 



B. Hypopygium more or less imbedded. 



Gen. XIII. Aiiepsius. Gen. XV. Syntormon. 



Gen. XIV. 4rgyra. 



II. First joint of the antennae entirely bare on its upper side. 



A. Third antennal joint in both sexes, or at least in the male, elon- 

 gated, tapering in a point, with an apical arista. 



A. Posterior transverse vein distant from the margin of the wing, 



palpi incumbent. 



Gen. XVI. Synarthrus. Gen. XIX. Xiphandrium. 



Gen. XVII. Systemis. Gen. XX. Porpliyrops. 



Gen. XVIII. Rhaphium. Gen. XXI. Smiliotus. 



B. Posterior transverse vein approximated to the margin of the 



wing ; palpi hanging down. 



Gen. XXII. Aphrosylus. 



