480 GEOLOGICAL SURVEY OF THE TERRITORIES. 



crown. Median three molars with a narrow posterior column, as in P. 

 agajjetillus. Punctate patch on inner face of ramus extensive. 



Measurements. 



Length of molar series = -016 



Length of median three molars - 010 



Width of median molar - 003 



Depth of ramus at median molar Oil 



This species and the last are rather larger than the prairie-marmot, 

 {Cynomys ludvicianus.) 



PEEISSODACTYLA. 



SYMBOEODON, Cope. 



Paleontological Bulletin, No. 15, p. 2, (August 20, 1873.)— Synopsis Vertebrata Col- 

 orado, 1873, p. 14. — Proceed. Amer. Assoc. Adv. Sci., 1873, p. 109. 



A genus embracing species, so far as known, of large size, allied to 

 Titanotherium, Leidy, and belonging to the same family. Its affinities 

 are indicated by the following description : 



Dental formula: I., I ; C, i; P. m. |; M., f . Teeth reduced in size an- 

 teriorly ; no diastema behind the canine. Molars consisting of two 

 external and confluent crescents, and one or two internal cones. In the 

 larger premolars, there are two, sometimes confluent, cones; in the mo- 

 lars, the posterior cone is sometimes much reduced, especially on the 

 third, while on the second and third a small third one is sometimes 

 added in front. The mandibular teeth are constructed like those of 

 Falceotherium^ i. e., of two crescents with the horns directed inward, 

 the middle two united, and the third molar with a third posterior one. 

 The superior incisors are very small and with obtuse crowns, and are 

 separated by a median interval ; the inferior canines are separated by 

 a short edentulous space, with thin alveolar margin openly emarginate. 



The cranium is remarkably elongate in proportion to its width, ex- 

 cepting in those species where the zygomas are so expanded as to modify 

 the proportions. The top of the skull is flat or convex in transverse direc- 

 tion, and the well- separated temj)oral fossse are overhung by the angular 

 or produced borders. The temporal fossae are well iiroduced posteriorly, 

 in some species remarkably so, and, with the supraoccipital border or 

 horizontal crest, inclose a deep occipital fossa. The inferior border of 

 the fossa is continued to the zygoma. The zygomatic fossa is rather 

 narrow, but the squamosal process is sometimes horizontally expanded 

 to a great mass. There are no postorbital processes, and in all the 

 species the orbits are small. The foramen infraorhitale is very large, 

 and is a simple perforation of the thin wall bounding the orbit in front. 

 A narrow column separates it from the orbit exteriorly, and a stouter 

 one from the external nasal meatus. The latter is large and very little 

 incised behind the premaxillary border. Hence the fore portion of the 

 nasal bones is very short. The lateral walls, anterior to the orbits, are 

 directed somewhat anteriorly, so that, viewed from the front, there is a 

 considerable border on each side of the nasal meatus, bounded by a lat- 

 eral vertical angle, and pierced below hj t\xQ foramen infraorbitale. The 

 borders of the nasal bones are thickened, and often ridged below. The 

 premaxillaries are small and fragile. 



The maxillaries rise above the level of the orbit in a solid support for 



