SYNOPSIS OF THE VERTEBHATE FAUNA OF THE PUERCO SERIES. 3-43 



TriSsodon biculminatcs sp. nov. 



Parts of the mandibular laini of two individuals indicate this species. One of 

 these supports the first and second true mohirs, and the other the lirst true molar 

 only. The character ol" the genus is seen in the great development of the external 

 cusp of the heel, and the absence of an internal cusp, so that the heel appears to have 

 one cusp with an oblicpie cutting edge, resembling in this respect Paheonyctis. The 

 two principal anterior cusps are opposite each other and united for half their eleva- 

 tion, and the internal is lai-ger relatively than in the T. quivirensis. The lif'th cusp 

 is low, forming a distinct tubercle in the first molar only, and represented by the in- 

 ternal anirle of an anterior led<>:e in the second. The heels of both the molars have three 

 small tubercles on the posterointernal border, which are not so much elevated as the 

 corresponding ones in the T. quivirensis. A weak external cingulum only. Enamel 

 obsoletely coarsely rugose with minute tubercles. 



Measurements. M. 



{anteroposterior Oil 

 transverse uuo 



f anteroposterior 013 



Diameters m. ii \ nnnr 



( transverse ouuo 



Depth of ramus iit m. i 020 



From the bottom of the Puerco beds. 



DISSACUS Cope. 

 Amer. Naturalist, 1881, p. 1019 ; Tertiary Vertebrata, 1885, p. 344, 741. 



Numerous pieces of the skeleton associated with molar teeth which agree with 

 those of the D. navqjovius, throw much light on its characters, and on the position of 

 the genus Dissacus. In the first place the zygapo])hyseal articulations of the lumbar 

 vertebrte are of the involute type common to all the Creodonta. This is also determinable 

 lioin the specimen described by uie in the Tertiary Vertebrata, p. 741. In the new 

 skeleton the fragments of metapodials, i)i-obably metatarsals, furnish evidence of the 

 existence of five digits, which distinguishes the genus from Mesonyx, where there are 

 but four. The astragalus is especially interesting in its relation to that of Mesonyx. 

 It has, as in that genus, a distinct cuboid facet, separated from that of the navicular 

 by an angle, but the angle is not as well defined as in >[esonyx and Pachyrena. 

 The trochlea is very .slightly concave, thus differing widely from that of the Meso- 

 nyehidie, and resembling that of other Creodonta. This bone therefore furnishes a 

 clear guide to the phylogeny of the Mesonychida). The two facets are well defined 

 on the proximal extremity of the cuboid. Its distal extremity supports but one, a 



A. I*. S. — VOL. XVI. 2k. 



