408 U. S. NATIONAL MUSEUM BULLETIN 2 1 6 part s 



The genus Listrognathus is probably almost worldwide. Most of 

 the species are Holarctic and Indo-Australian. It is divisible into 

 four subgenera, as keyed and described below. 



Key to the subgenera of Listrognathus 



1. Thyridium narrow, about 0.8 as wide as its distance from base of second tergite; 



clypeus in profile moderately convex, not sharply pyramidal; lower end of 

 occipital carina moderately incurved, joining hypostomal carina at an acute 

 angle; apical transverse carina of propodeum not interrupted medially. 



Nearctic 1. Fenestula, new subgenus 



Thyridium wide, about 1.3 to 2.5 as wide as its distance from base of second 

 tergite; clypeus pyramidal in profile 2 



2. Lower end of occipital carina curved sharply toward the hypostomal carina 



or more or less recurved, joining hypostomal carina at a right angle or 

 recurved and more or less interrupted at hypostomal carina, the hypo- 

 stomal carina very high; shoulders on upper edge of pronotum moderately 

 strong, usually obtuse; second tergite usually with a yellow or white apical 



band. Holarctic and Oriental 4. Listrognathus 



Lower end of occipital carina curved rather weakly toward hypostomal carina, 

 which it meets at an acute angle; shoulders on upper edge of pronotum 

 very strong, usually acute; second tergite usually with an interrupted yel- 

 low or white apical band or a pair of lateral spots 3 



3. Lower lateral edge of first abdominal tergite without teeth; postpetiole mod- 



erately wide to very wide. Indo-Australian 2. Suvalta 



Lower lateral edge of first abdominal tergite with one or two strong teeth 

 near its midlength; postpetiole very wide. Indo-Australian . 3. Stivadens 



1. Fenestula, new subgenus 



Front wing 5.4 to 8.0 mm. long; clypeus moderately convex, in 

 profile not pyramidal or with only a trace of a median point; lower 

 end of occipital carina moderately incurved, joining hypostomal 

 carina at an acute angle, not recurved or interrupted; hypostomal 

 carina not unusually high; shoulders on upper edge of pronotum 

 moderately strong, obtuse ; apical transverse carina of propodeum not 

 interrupted mechally, forming only weak apophyses; lower edge of 

 first tergite simple; thjo-idium narrower than its distance from base of 

 second tergite; upper valve of ovipositor beyond nodus not strongly 

 depressed. 



The subgeneric name is from Latin fenestra (window) plus ula 

 (diminutive), in allusion to the small thyridiiun. 



Genotype: Mesostenus paludatus Cresson, 1872. 



This subgenus includes one widespread Nearctic species. 



1. Listrognathus (Fenestula) paludata (Cresson) 



Figure 329,i 



Front wing 5.4 to 8.0 mm. long; propodeum almost horizontal 

 basad of its apical carina, abruptly declivous at its apical carina; 



