ON THE REPTILIA OF PERU. 183 



behind by five wide smooth scales. Scales of the top of the head smaller, sub- 

 hexagonal, and smooth. Inferior labials ten, all wider than long. Scales of the 

 body not elongate, in twenty-three longitudinal rows, the lower one or two rows 

 smooth, the remainder keeled, but differently from what is observed in other spe- 

 cies. Thus the keels do not reach the extremity of the scale, but terminate in an 

 enlargement, which, on the posterior parts of the body, is a prominent tubercle. 

 Gastrosteges 159 ; anal entire; urosteges 52. 



Color above yellowish-brown, anteriorly uniform, and marked on the posterior 

 two-thirds of the body with brown triangles on the sides, whose apices meet or 

 approach on the middle line above. The interior at the base of the triangle is 

 occupied by the ground color, which increases in extent anteriorly, so as to reduce 

 the triangles to skeletons, and then obliterate them. Posteriorly the united tri- 

 angles form cross-bands, which become united lengthwise on the tail, and finally 

 confluent so as to form a uniform black. Head yellowish-brown above, yellow 

 below, a yellow band extending from the eye to the side of the neck, which is 

 bounded all the way by a brown band below. Belly yellow anteriorly, shaded 

 increasingly with black to the end of the tail, a dark brown spot on the end of 



every second gastrostege on each side. 



M. 

 Length 885 



Length of tail 125 



" of rictus oris ......... .038 



" to eye 013 



Width between eyes . . . . . . . . . .017 



Diameter of eye (greatest) . . . . . . , . .005 



From between Balsa Puerto and Moyabamba, Peru. 



This pit-viper is evidently a dangerous species, judging from the large size of 

 its venom glands and length of its fangs. Associated with the development of 

 the former, is the very small size of the eye, which is almost closed by the pro- 

 tuberant cheeks. The species is allied to the B. diporus. Cope, and B. 7ieuvidn, 

 Wagl. It differs, among other respects, in the smooth scales of the* vertex, large 

 in front and small behind. 



