108 U. S. NATIONAL MUSEUM BULLETIN 216 



is nearly always entirely black. Many of the species are difficult to 

 distinguish, and have very frequently been misdetermined. The keys 

 and descriptions below are the best that we could devise, but are not 

 adequate for distinguishing a large portion of the males, and an occa- 

 sional female is not determinable with the known characters. 



Keys to the Nearctic species of Triclistus 



MALES 



(Males of Melanoeephalus, chosis, and adustus are unknown.) 



1. Hind spur of hind tibia (including its hairs) about 3.0 as long as wide; punc- 



tures on face rather fine, separated by about 0.4 to 0.8 their diameter. 



PODAGRICUS GROUP 2 



Hind spur of hind tibia (including its hairs) about 4.0 to 5.0 as long as wide; 

 punctures on face rather coarse, separated by about 0.25 to 1.0 their diam- 

 eter. Crasstjs group 3 



2. Hind coxa mostly blackish; third and fourth tergites with hairs medially 



(but not apically) 10. podagricus (Gravenhorst) 



Hind coxa entirely ferruginous; third and fourth tergites without hairs 

 medially 11. pallipes Holmgren 



3. Hind coxa black; costula present, at least as a stub. 



2. brunnipes (Cresson) 

 Hind coxa fulvous or ferruginous 4 



4. Costula complete; outer side of second lateral area of propodeum about 1.9 



as long as inner side; tegula usually more or less fulvous, but sometimes 



entirely yellow 1. crassus, new species 



Costula complete, incomplete, or absent, if complete the outer side of second 

 lateral area of propodeum about 1.4 as long as inner side; tegula yellow. 1 



3. emarginalus (Say) 

 4. occidentis, new species 



5. rectus, new species 



6. cvexus, new species 

 8. propinquus, new species 



9. chosis, new species 



FEMALES 



1. Median third of fourth abdominal tergite with no hairs or with only a few 



scattered hairs (figs. 186,g,h) ; hind spur of hind tibia (including its hairs) 



about 2.8 to 3.8 as long as wide. Podagricus group 2 



Median third of fourth abdominal tergite with numerous, regularly spaced 

 hairs (fig. 186,f); hind spur of hind tibia about 4.0 to 5.0 as long as wide. 

 Crassus group 5 



2. Body ferruginous; median longitudinal carinae of propodeum lacking except 



for short weak stubs basally and on apical transverse carina (fig. 187,k). 



12. melanoeephalus (Cameron) 



Body black; median longitudinal carinae of propodeum distinct (figs. 187, 



i, and j) 3 



i We have not been able to make a clear separation between the males of these species, though with the 

 aid of certain variable characters, distributional information, and associated females, one can determine 

 some of the males with probably accuracy. 



