404 Mr. D. Sharp's Contributions to the 



is a matter of great difficulty. The characters by which 

 the sexes may be distinguished are extremely slight; in 

 some species the antennie are very elongate in some male 

 specimens, but in other individuals scarcely diiFer at all 

 li'om those of the female, "while the structure of the {edeagus 

 shows scarcely any variation in very dissimilar species. 



1. Picstus valid us, n. sp. Niger, nitidus, subdepressus, 

 abdominis apice piceo ; antennis setosis, articulis 1, 3, 4 

 et 5 setis intus densioribus ; fronte bispinosa, spinis 

 approximatis ; prothorace sat crebre obsolete punctato. 

 Long. Corp. 6 lin. 



Antennae blackish, rather stout, 2^ lin. in length, 

 clothed with tawuy, elongate seta). These setaa are specially 

 long and dense on the inner side of the 1st, 3rd and 4tli 

 joints, while the 5th joint is less setose than the 4th, but 

 more than the 6th. Front of head armed with two mode- 

 rately long acuminate spines ; behind these the head in the 

 middle is depressed, the depression shaped somewhat like 

 a narrow V ; the spines at nearly half their distance from 

 the base are only separated by a width of about ^V of 

 a line ; the sui'face is sparingly and finely punctured. 

 Thorax 1 lin. iu length, 1^ lin. in breadth, channelled 

 along the middle, transversely a little convex ; the surface 

 very shining, and with rather numerous, but obsolete 

 punctures. Elytra shining black, 1| lin. in length, their 

 greatest breadth just that of the thorax, viz.. If lin., each 

 with 5 deep strije, and outside these with indications of a 

 Oth stria sufficiently well marked at the extremity. Hind 

 body black, not very shining ; the segments punctured at 

 the base and sides of each, the basal segment nearly 

 entirely coriaceous ; the extremity pitchy yellow, the 

 paler colour commencing on the hind part of the 6th 

 segment. Legs black, with the tarsi pitchy. 



Pebas ; three specimens, 2 S , I $. 



Obs. I. — There are several species of Piestus mixed in 

 descriptions and collections under the name of P. bicornis. 

 I have not, however, seen the above-described species from 

 any other locality than this of the Upper Amazons ; its 

 large size, together Avith its distinctly punctured thorax, 

 distinguish it from all the closely allied forms. 



Obs. IT. — I have ascertained the sexes of this species 

 by dissection, Avithout which they cannot be distinguished. 

 Of the two males, one has the thorax remarkably develojjed. 



