54 DIPTERA OF NORTH AMERICA. [PART IV. 



seldom short subcylindrical (as in D. immodesta, gladiator) ; with 

 moderately long, often inconspicuous verticils (in the two species 

 just named, the verticils are somewhat longer than usual). The 

 collar is broad, well developed, triangular at a side-view ; with 

 a neck-like prolongation, carrying the head ; thoracic suture well 

 marked. The feet are slender, with a very inconspicuous, almost 

 microscopic pubescence, and, as a general rule, of a uniform 

 coloring. Most of the species have a distinct tooth on the under 

 side of the ungues, near the basis, sometimes followed by a 

 smaller one. In D. defuncta, these teeth are replaced by a few 

 notches on the under side of the ungues. In some species, as in 

 D. hseretica, the teeth are very small and difficult to perceive. 



The venation follows rather closely a certain uniform type, and 

 but few of the characters taken from it can be used for the dis- 

 tinction of the species. The auxiliary vein generally ends in the 

 costa nearly opposite the origin of the second longitudinal vein ; 

 in some species it is still shorter and ends before the origin of the 

 second vein (D. rostrifera, brevivena, and floridana), and it is 

 an exception when it reaches considerably beyond the origin of 

 that vein (D. defuncta, pubipennis, rara, globithorax). The 

 distance of the subcostal cross-vein from the tip of the auxiliary 

 vein, which is variable, affords good specific characters. The 

 first longitudinal vein ends in the costa near the posterior end 

 of the stigma, nearly opposite the tip of the fifth longitudinal 

 vein and more or less beyond the inner end of the submarginal 

 cell ; often at one-third, at the utmost about the middle of this 

 cell ; the marginal cross-vein is close at the tip of the first longi- 

 tudinal vein ; in most species, this cross-vein forms a nearly 

 straight line with the tip of the first longitudinal vein ; often, 

 however, the upper half of this straight line recedes a little back- 

 wards and in such cases it appears as if the first longitudinal vein 

 was incurved towards the second and ended in it, while the cross- 

 vein in such a case seems to connect the first longitudinal vein 

 with the costa. Such is the case with D. pubipennis (Tab. I, 

 fig. 2) and globithorax ; sometimes this character is not specific, 

 but merely adventitious. The course of the second longitudinal 

 vein varies in the relative length of the two portions of this vein, 

 before and after emitting the third vein. The inner portion or 

 the praefurca is remarkably short in those species which have a 

 very short auxiliary vein {D. rostrifera, brevivena, floridana). 



