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On the classification of North American Diptera 



(Second paper.)* 

 By Dr. S. W. Williston. 



The limits of the two following families, as here given, are narrower 



than these now accepted by Osten-Sacken, whose authority in dipterologi- 

 cal matters I need not say is among the very highest. For convenience 

 sake, however, I exclude certain disputed genera, to be discussed else- 

 where, thus rendering the forms given in this paper more certainly re- 

 cognizable. In this, as in the following papers, I introduce genera from 

 Mexico and the West Indies, wherever I can do so with clearness; such 

 will be printed in italics. Genera unknown to me will be preceded b\ 

 .in asterisk. 



TANYSTOMA. 



Tarsi with three membranous pads at the tip (the empodium deve- 

 loped pulvilliform); body and legs wholly without macrochaetae {diptera 

 eremochceta Osten-Sacken); eyes of male holoptic (Osten-Sacken), rarely 

 narrowly seperated; two sub-marginal, five posterior cells in the wing, 

 fifth posterior cell not contiguous at its base with the discal cell; the mar- 

 ginal vein encompasses the whole wing; some or all the tibiae with spurs. 



TABANIDiE. 



Proboscis of the male with four, of the female with six bristles; third 

 joint of the antennae annulate, never with differentiated style or bristle; tegu- 

 Idt rather large. 



Species never very small, often among the largest in the order; never 

 thickly pilose; in life the eyes usually brilliantly colored and marked. 

 Head short, broad, eyes large. Antennae porrect, the third joint com- 

 posed of from three to eight annuli or segments. Thorax not very 

 convex, scutellum without spines on its border. Abdomen broad, 

 moderately elongate or short, never slender or contracted. Legs moder- 

 ately stout, the front and middle tibiae sometimes dilated, the middle 

 tibiae always with spurs. Veins of the wings distinct: first posterior cell 

 (and fourth in exotic species) rarely closed. 



Early stages passed in the water or earth; larvae carnivorous; with 

 a distinct head; pupae free. The females are blood-sucking, usually found 

 in the neighborhood of pastures, in sunny open parts of woods, during 

 the hot sun-shiny days of summer. The males are much more rarely 

 met with, and will be found usually in sweepings of meadow lands, on 

 flowers, etc. 



* The first paper of the series is in Bull. B'kl. Ent. Soc. VII, p. 129. 



