from the Tertiary deposits of Wyoming. 



the centrum, and is less rounded. The hjpapophysial ridge, 

 also, is sharper, and extends nearer to the inferior edge of the 

 articular ball. 



From the vertebra? of Dinophis Marsh, which genus includes 

 the only fossil Ophidians hitherto found in this country, as well 

 as from those of the nearly allied Pakeophis of Owen, the speci- 

 mens of Boavus here described are widely separated, especially 

 by their greatly inferior size ; by the shorter neural spine ; bj 

 the broader zygosphene, which exceeds in transverse diameter 

 the articular cup, as in most modem serpents ; by the elevation , 

 extending backward from the zygosphene ; by the more expan- 

 ded diapophyses ; and by the well developed lateral and inferior 

 median ridges on the centrum. The vertebrae of Boavus, how- 

 ever, resemble those of Palceophis and Dinophis, and differ from 

 those of Boa, Crotalus, and many other modem serpents, in hav- 

 ing the sides of the neural canal extended forward nearly to the 

 edge of the articular cup. 



Boavus occidentalism sp. nov. 

 This species is established on eight vertebrae, nearly all from 

 the middle dorsal region. They evidently represent several 

 individuals, as they differ considerably in size, and were found 

 at three separate localities. They indicate constricting serpents 

 between six and eight feet in length. The neural arch in this 

 species is elevated and massive. The neural spine is short, and 

 tnangular at its base, which rests on the posterior three-fourths 

 of the arch. The zygosphene is convex above, slightly ex- 

 cavated in front, and without a median tubercle. The neural 

 canal has a distinct median epapophysis on its floor, and sharp 

 lateral ridges, which give it a sub-trifoliate outlme. The dia- 

 pophyses are auriform, and project below the inferior margin of 

 the cup. The h3rpapophysis is a sharp ridge, beginning at the 

 margin of the cup, and ending, just before reaching the ball, in 

 an obtuse projection. 



I he principal dimensions of one of the largest vertebrae of 

 this species are as follows:— 

 Length of centrum from edge of cup to convexity of ball, 4-50 lines. 



i^ransverse diameter of cup, --- ---- 2-80 " 



Verticaldiameter of cup,.": - — 2-50 « 



ransverse diameter of zygosphene at base, 3-50 " 



istance from top of zygosphene to lower margin of cup, 5- " 



^ertical diameteV of ball, 2-45 « 



vvidth of neural canalin front,--.. - l''^^ " 



*leight of neural canal in front, - MO « 



. The various specimens representing this species were found 

 in September last by H. B. Sargent, A. H. Ewing, and the 



