StdpliijUuida: of the Amazon Valley. 117 



In this genus the sexual characters become remarkable, 

 and are Avell worthy of study, for they appear to me to 

 suggest the functional result of some very remarkable 

 modifications. The specimen of P, Traili here described 

 was received by me in spirit in very fresh condition ; and 

 by dissecting out the apical segment, and mounting it im- 

 mediately in Canada balsam, the structure of the hard and 

 soft parts of the intromittent organ are finely displayed, as 

 well as their position in relation to the lateral valves. 



1. Plocioptcrus tricolor, n. sp. Niger, nitidus, antennis 

 articulis ultimis quatuor pallidis, abdominis apice rufo- 

 testaceo ; elytris cyaneis fasciis duabus, abdomineque 

 fascia singula cinereo-tomentosis. Long. corp. 6 — 7 lin. 



Mas : abdominis segmento sexto ventrali linea media 

 transversali dense longeque testaceo-pilosa instructo, mar- 

 gineque apicali leviter emarginato, segmento 7° apice 

 medio late triangulariter emarginato ; tarsis anticis sim- 

 plicibus. 



Ohs, — Mares majores, elytris linea lateral! elevata lon- 

 gitudine variabilc instructis, insignes. 



Antennre slender, elongate, black, with joints 8 — 11 

 pale yellow ; 3rd joint very long, about twice as long as 

 the 4th; 4th about equal to 2nd in length; lltli joint 

 oblong, longer and narrower than the preceding one. 

 Head broader than the thorax, black, shining, coarsely 

 and irregularly punctured ; the punctures so disposed as to 

 leave a small triangular space behind the labrum, and a 

 large irregular space on the disc, free ; the punctures armed 

 witli fine greyish setas. Mandibles and palpi elongate, 

 black or pitchy-black. Thorax about as long as broad, 

 much narrower than the elytra, a little narrowed behind, 

 the hind angles quite rounded, the sides scarcely sinuate ; 

 it is black and shining, coarsely and irregularly punctured, 

 a broad irregular smooth space in the middle free ; the 

 punctiu'es are finer at the sides. Scutellum large, dull, 

 closely and finely punctured, clothed Avith a dense grey 

 jDubescence. Elytra longer than the thorax, blue, rather 

 closely and finely punctured, clothed at the base and apex 

 with a dense grey pubescence. Hind body narroAver 

 toAvards the extremity, black, with the 6th and 7th seg- 

 ments bright yelloAV ; 2nd segment impunctate, 3rd finely 

 and rather closely punctured, and clothed Avith a grey 

 pubescence ; 4 and 5 finely and not closely punctured, 



