CERAMBYCIDAE. 9^3 



beneath in Derohrachus hrevicollis; densely punctured, some- 

 what rough in D. geminalus ; hind femora less deeply snlcate 

 beneath, and with several short elevated ridges on the inner sur- 

 face in Orthosonia. In both genera the narrow epipleural por- 

 tion of the elytra is transversely striate, forming a stridulating 

 organ upon which the ridges or edges of the hind femora grate 

 to produce a sound. 



Among our three species we recognize but two genera, Dcro- 

 brachus and Orthosoma, distinguished sufficiently by the char- 

 acters above givtai. Braderorhus Buquet, to which D. gemi- 

 natus Lee. has been referred, does not seem to us sufficiently 

 distinct. Besides tiie sexual characters above mentioned, the 

 5th segment in the % of Derobraehns is broadly emarginate, the 

 fith visible and also emarginate ; and the last dorsal is truncate 

 and emarginate ; the 5tli ventral is elongate and truncate in the 

 9, but the 6th is not visible. 



In Orthosoma the 5th ventral is rounded in the 9, but broadly 

 truncate in the %, leaving the fith visible. 



The distribution of the species is as follows: — 



Derohrachus hrevicollis, Southern States. 



D. geminatus from Texas, through Arizona to Ijower California. 



Orthosoma hrunneum Forst. (cylindricuni Fahr.), is generally 

 distributed over the Atlantic States. 



Tribe IV.— PRIOXIXI. 



In this tribe the mandibles are moderate in size, acute, and 

 similar in both sexes. The eyes are coarsely granulated, usually 

 large, transverse, convex, and approximated. The antenna? have 

 from 12-2'7 joints, varying according to species, the joints are 

 conical and imbricated, mucii heavier in the % than the 9, the 

 poriferous system conmiences on the 3d joint, and covers nearly 

 the whole surface of the 4th and following joints. In r'rioiius 

 % and 9 the sensitive surfa(!e is reticulate, with fine elevated 

 lines, but in Homapsthesis %, the surface is quite uniform. The 

 sides of the prothorax are armed with 3 acute teeth in Prionus, 

 but in Homsesthcsis iiiiegra and emarginala the apical and basal 

 teeth are obsolete, so that the sides become unidentate. 



P. palparis Say has the form of Trionus, but the antennie 

 are as in IIom«sthesis. 

 18 



