153 



NORTH AMERICAN DIPTERA. 



mented style or arista, altogether not more than eight 

 (19); (4) the third joint simple, with or without a ter- 

 minal or dorsal arista (7, 9). Veins of the wings distinct, 

 not crowded anteriorly; third longitudinal vein furcate; 

 basal cells large; five posterior cells usually present. 



As defined above, this family includes the Xylophagi- 

 dae, L,eptidae and Coenomyidse of authors. It may be a 

 question whether this union is justifiable, but, on the 

 whole, it seems that the sole character which can be used 

 to distinguish the families the structure of the third 

 antennal joint divides the group unnaturally, throwing 

 with the Xylophagidae forms whose affinities are great- 

 est with the lyeptidae, notwithstanding the antennal char- 

 acter. 



The Xylophaginae include less than one hundred 

 known forms, and many of them are remarkable for their 

 general resemblance to certain hymenopterous insects. 

 Species of Rhachiccnis form a connecting link with the 

 Nemocera, and are apt to be confounded with the Rhyph- 

 idse, but the presence of the pulvilli will distinguish 

 them. 



The larvae are found in decaying wood or under the 

 bark of trees and are carnivorous and predaceous, feed- 

 ing upon the larvae of beetles and other wood insects. 

 The skin is parchment-like, the body cylindrical. The 

 mouth-parts and antennae are very small, the maxillae 

 short and hook-like. The first cr the first three segments 

 back of the head are chitinized above; the last segment 

 above with a chitinized plate terminating posteriorly in 

 two hooks. The fourth to the ninth segments have bristly 

 pseudopods below. The pupae are free. Larvae of Xylo- 

 mvia have been observed under the bark of fallen cotton- 

 wood trees. 



The Leptinae comprise something over two hundred 

 known species. They are usually of moderate size and 



