926 Charles Paul Alexander 



4. Coloration grayish brown, the proscutum with three dark brown stripes; abdomen dark 

 brown with paler caudal margins to the segments; wings very pale brown, the radial 

 sector very short, arcuated, angulated, or spurred. [Proc. Acad. Nat. Sci. Phila., 



p. 543-544, pi. 2S, fig. 57. 1916.] (Plate XLI, 173.) R. cayuga Alex. 



Coloration reddish brown, the prescutum with three indistinct stripes; abdomen yellowish 

 brown, the hyp^pygium bright yellow; wings nearly hyaline, the radial sector somewhat 

 elongated, slightly arcuated. [Proc. Acad. Nat. Sci. Phila., p. 544-545, pi. 28, fig. 58. 

 1916.] (Plate XLI, 172.) R. rubescens Alex. 



SUBFAMILY CyHndrotominac 



The genera of the subfamily Cyhndrotominae may be separated in 

 accordance with the following key: 



1. Head and intervals of the prescutum with numerous deep punctures. 



Triogma Schin. (p. 926) 

 Head and intervals of the prescutum smooth 2 



2. Three branches of the radius reaching the wing margin. 



Phalacrocera Schin. (species neoxena Alex.) (p. 927) 

 Two branches of the radius reaching the wing margin, caused by an apparent fusion 



of /?l-f2+3 3 



3. Three branches of the media reaching the wing margin. . , .Cylindrotoma Macq. (p. 927) 

 Two branches of the media reaching the wing margin 4 



4. Cross-vein r-m present; cross- vein m obliterated by the fusion of Ms on Afi+2; antennae 



of male tipuline in structure Phalacrocera Schin. (species tipulina O. S.) (p. 927) 



Cross-vein r-m usually obliterated by the fusion of 7^4+6 on M1+2; cross-vein m present; 

 antennae of male subpectinate, the individual flagellar segments almost cordate. 



Liogma O. S. (p. 927) 



Genus Triogma Schiner 



1S63 Triogma Schin. Wien. Ent. Monatschr., vol. 7, p. 223. 



There are but two known species of Triogma, one occurring .in Europe 

 and the other in northeastern North America. The larval life of the 

 European species, the only one that is known, is spent on aquatic mosses 

 growing in mountain torrents. The insects closely resemble the species 

 of Liogma in all their stages. 



Triogma exculpta O. S. 



1865 Triogma exculpta 0. S. Proc. Ent. Soc. Phila., vol. 4, p. 230. 



Triogma exculpta is a rather small, dull brown fly, with the wings suffused 

 with brown. The head and the sides of the thorax are deeply punctured. 

 The fly is rare and is insufficiently known. The venation is very much 

 like that in the genus Liogma. (Johnson, 1909: 13L) 



