6 U. S. NATIONAL MUSEUM BULLETIN 216 



Trieces, and Chorinaeus. Exochus, Triclistus, and Colpotrochia, how- 

 ever, seem to be mostly in forests, and the pictus, montivagus, and 

 tibialis species groups of Exochus are mostly in damp forests. 



The subfamily is generally distributed through the world, from the 

 arctic to the tropics, in dry and in wet climates, and in all the larger 

 faunas. . All the larger genera (Chorinaeus, Trieces, Metopius, Tri- 

 clistus, Colpotrochia, Hypsicera, and Exochus) are essentially world- 

 wide, though Hypsicera is represented in the Neotropics by only two 

 introduced species. The smaller genera also tend to have a wide 

 range. All but three of the known genera and three of the subgenera 

 occur in the Nearctic Region, a fact which has prompted the inclusion 

 of the missing ones in this revision, to make the generic and sub- 

 generic treatment worldwide in scope. 



Key to the genera of Metopiinae 



1. Face occupied largely by a flat or concave escutcheon-shaped area bounded 



by a carina (figs. 166,b-169,b); middle tibia with one spur. Worldwide. 



6. Metopius (p. 59) 



Face entirely convex; middle tibia with two spurs except in male of 



Acerataspis 2 



2. Epipleura of third to fifth abdominal tergites apparently absent (represented 



by narrow, inconspicuous vestiges) ; front and middle tarsal claws con- 

 spicuously pectinate 3 



Epipleura of third to fifth tergites well developed; front and middle tarsal 

 claws usually apparently simple 7 



3. Areolet present; interantennal process of face forming a high semicircular 



flange between antennal sockets; second abdominal tergite with a pair 

 of median longitudinal carinae; seventh tergite of male retracted; hind 

 tarsal claws conspicuously pectinate; front wing 7 to 10 mm. long ... 4 

 Areolet absent; interantennal process of face forming a triangular projection 

 in front of antennal sockets, but not a high flange between them; second 

 abdominal tergite with a median longitudinal carina (except in the Euro- 

 pean Chorinaeus talpa) and often also with sublateral longitudinal carinae; 

 seventh tergite of male exposed; hind tarsal claws apparently simple; 

 front wing 2.6 to 7 mm. long 5 



4. Abdomen parallel-sided, the fifth and sixth segments not wider than the 



preceding segments, and the apex of the sixth segment not specialized 

 (fig. 164,a); middle tibia of male with two spurs. Eastern Nearctic and 



eastern Palaearctic 1. Pseudometopius (p. 8) 



Abdomen clavate, the fifth and sixth segments much wider than the preceding 

 segments, the apex of the sixth segment subspherically rounded (fig. 164,b) ; 

 middle tibia of male with one spur. Oriental . . 2. Acerataspis (p. 11) 



5. Scutellum quadrate, its lateral carina strong and produced apically into a 



prominent tooth; abdomen clavate, progressively enlarged from its base to 

 the fourth and fifth segments; posterior mesosternal carina complete, not 

 interrupted in front of each middle coxa. Ethiopian. 



5. Hemimetopius (p. 59) 



Scutellum parabolic in outline, its lateral carina low, rarely produced apically 



as a small tooth; abdomen parallel-sided; posterior mesosternal carina 



interrupted in front of each middle coxa 6 



