CERAMBYCIDAB. 297 



Tribe IX.— TRACIIYDERIXI. 



A very large tribe as here defined, and containing as great a 

 variety of forms as the Cerauibycini, from wliieli it is distinguislied 

 by the acntely triangnlar scutelhmi, and finely granulated eyes. 

 The last joint of the palpi never has the triangular form which it 

 affects in most Cerambycini, but is usually oval, squarely truncate 

 at tip, with a deep elliptical impression on the side.* The tilji;e 

 are not carinate, and the tibial spurs are rather long. 



The following grou})s may be recognized in our fauna: — 



Mandibles acute, or simple at tip ; 



Pronotum broadly lobed at base ; poriferous system of antennas very 



distinct ; 



Metasternal pores absent, side pieces very wide. Meg.xderi. 



Metasternal pores distinct. Trachydkees. 



Pronotum not lobed, sometimes subsinuate at base, i)oriferous system 



often obsolete, and palpi in some genera scarcely impressed. 



Stenaspes. 

 Mandibles emarginate at tip. Tyloses. 



Group I. — Megaderi. 



This group contains but one genus Megaderus, of which one 

 species, M. bifasciatus Dupont (corallifer Newm.), extends from 

 Mexico into Texas. It is a broad, flat insect, with roughly 

 punctured prothorax, angulated on the sides behind the middle; 

 elytra finely punctured, with a basal and medial transverse band, 

 which are more or less confluent, sei)arate, or even obliterated. 



The antennae are shorter than the body, with the 1st joint as 

 long as the od, and a little thicker; 3d and following with porif- 

 erous spaces; outer joints velvety, 11th appen<liculate, acute at 

 tip; front rather flat, oblique; geme long; mandibles stout, acute, 

 palpi short, last joint not elongated, oval truncate, deeply im- 

 pressed. Prothorax broad, strongly and broadly lobed at the 

 base, deeply excavated behind the middle, especially at the sides, 



* Among the Cerambycini with coarsely granulated eyes this form of 

 palpi may be observed, and the lateral fovea in Chion, which is an annec- 

 tent form ; and the same in a much less degree in some other genera. The 

 maxillary palpi are never short as in Callichromini, nor has tlie % an 

 additional ventral segment. The front coxal cavities are open behind, 

 and not angulated externally. 



