133 



Family Rachiceridae 



Flies of medium size, elongated, very thinly pilose, resembling saw- 

 flies. 



Males diclioptic. Empodium developed pulvilliform, the piilvilli 

 present. Antennae composed of twenty to thirty-eight segments, often 

 strongly serrate. Squama? small or rudimentary. Veins strong; discal 

 cell three times as long as wide; fourth posterior cell closed and petio- 

 late; anal cell closed apieally. Legs moderately long. 



The only genus belonging to this family is Rachicerus Walker of 

 which only about a score of species are known. Six species have been 

 described from the Nearctic region, but one is unrecognizable. 



The lar\-£e are found in decaying wood and are presumed to be 

 predaceous. 



Rachicerus has usually been placed in the Rhagionidce (s. 1.) but 

 should no doubt be isolated since the large number of antennal seg- 

 ments, all of which are freely articulate, indicates a more primitive 

 condition than that accorded even the Coenomyiidffi of the present work. 



KEY TO NEARCTIC SPECIES OF RACHICERUS 



1. AntenriEe reddish toward the base, pectinate below, the lower processes 



conspicuously long-er than the upper obscuripenis Lcew 



Antennae not reddish basally, the lower processes on the segments 

 short, at most slightly longer than the upper 2 



2. Mesonotum brownish yellow, sometimes with brown vitt^, never 



blackish -t 



Mesonotum black or brownish black 3 



3. Halteres yellow; wings hyaline with a dark median cloud in front; 



mesonotum shining black nitidus Johnson 



Halteres brownish; wings tinged with brown; mesonotum shining 

 dark brown niger Leonard 



4. Mesonotum without brown vittae; ? antennte serrate, with 21 or 22 



segments, d antennae sub-pectinate below, with 28 to 35 segments. 



fulvicollis Haliday 

 Mesonotum with two broad brown vittae; antennae sub-pectinate be- 

 low, with 22 or 23 segments honestus Osten Sacken 



Rachicerus, head and wing. 



