362 COLEOPTERA OP NORTH AMERICA. 



Our genera may be arranged in the following manner: — 

 Mandibles usually toothed above, clasping the middle lobe of the epistoma, 

 not concealed, labrum concealed or feebly prominent. 



Group Triorophi. 

 Intercoxal process of abdomen broad, feebly narrowed in front, tip sub- 

 truncate or rounded ; 

 Tarsi spinous beneath ; hind tarsi with joint 1 equal to 3 and 4 

 together ; 

 Middle lobe of front narrowed at base, and clasped by a tooth-like 

 . process from the base of the mandibles. Triorophus. 



Middle lobe of front triangular, much narrowed in front, mandibles 

 without basal tooth. Stibia. 



Tarsi with silken hairs beneath ; hind tarsi with first and fourth 

 joints equal. 

 Middle lobe of front narrower anteriorly, mandibles without basal 

 tooth, thorax narrower in front. Triphalus. 



Intercoxal process of abdomen triangular, acute or oval at tip ; tarsi 

 spinous beneath ; 

 Middle lobe of front narrowed anteriorly, either oval or truncate. 



Trimytis. 



Mandibles not toothed above, not clasping the middle lobe of front which 



is broad and emarginate, and conceals the mandibles in repose ; 



labrum prominent. Group Auchmobii. 



Intercoxal process oval at tip ; tarsi spinous beneath. Auchmobius. 



These genera are represented by a few species, at most, in 

 each, which occur west of the region of northern Texas and 

 Nebraslia. Trimytis is closely related to Trientoraa, but differs 

 in having the eyes partially divided by the sides of the front. 

 The other genera have no very close foreign allies. Auchmobius 

 leads naturally to the following tribe. 



Tribe IV.— THIIVOBATIIVI. 



Body oval or rounded, sometimes winged; epistoma truncate, 

 or feebly rounded; labrum prominent, or not; nientum very large, 

 entirely filling the gular cavity; ligula and maxillae concealed; 

 elytra not widely embracing the flanks of the abdomen ; pro- 

 sternum not adapted to the mesosternuni ; metasternum some- 

 times elongated; middle coxfe without trochantin, inclosed by the 

 sterna ; hind coxre approximate, intercoxal process of the abdo- 

 men acute. Tarsi ciliate beneath. 



Our genera may be thus tabulated : — 



Anterior tibire with the outer angle prolonged. Eurymetopon. 



Anterior tibiae truncate at tip. Emmenastus, 



