GEOLOGICAL SURVEY OF THE TERRITOEIES. ' 611 



mandibular cutters are less widely separated by a narrow prolongation 

 of the symphysis. The exposui-e of the tooth is lateral, its direction 

 nearly anterior. It projects anteriorly very little beyond the synaphysis, 

 and has a horizontal triturating surface below the level of the latter. 

 There are alveolae for but three molar teeth, each with three roots. 

 The teeth themselves are not contained in them, but were apparently 

 lost before the cranium was entombed in the Eocene mud. The posi- 

 tion of the first molar is occupied by spongy bone in both maxillaries, 

 and appears as though such teeth might have existed earlier in life and 

 been shed. The pterygoid laminae are prolonged, inclosing a trough. 

 The fo7'ame7i ovale is well developed and simple, and bounded behind 

 and before by a ridge. There are no additional foramina in this region. 

 The space for the otic bulla is moderately large; the basicranial axis is 

 grooved at the junction of the basi-occipital and sphenoid bones. The 

 zygomatic arch is deep and thin. The glenoid cavity is wide but lon- 

 gitudinal. The cast of the brain indicates smooth oval hemispheres 

 which leave the cerebellum and olfactory lobes entirely exposed. The 

 latter are ovoid and expanded laterally. This genus is allied to, if not 

 actually a member of, the Sciuridcc. The breadth and depression of its 

 form reminds one of Arctomys, but the contraction behind the orbits is 

 very different, resembling rather the form of Fiber. The lateral separa- 

 tion of the incisors, superior and inferior, is a marked peculiarity. 



PSEUDOTOMUS HIANS, CopC. 



Loc. eit. 



The enamel of the superior incisors is not grooved, but has a delicate 

 striate sculpture. The inferior incisor does not project as far as the 

 alveolar border of the jaw ; its surface worn by the upper incisor is hor- 

 izontal and anterior. The inferior diastema is a thin edge, and the 

 ramus is deep there. The temporal surface of the parietal bones is 

 rugose. The cranium is depressed, and has a trace of interparietal crest. 

 The anterior margin of the temporal fossa is marked by a curved angle 

 on each side of the frontal bone. The supra-orbital arch is very short. 



Measure77ients. 



M. 



Length cranium, (3.75 in.) 0.095 



Width cranium, (without zygomas) 040 



Width cranium, (with zygomas) , 072 



Width of occiput 032 



Width cranium near end of nasals 027 



Width upper cutting tooth 007 



Depth upper cuttiug tooth 0085 



Length exposed part lower tooth 009 



Width exposed part lower tooth 006 



From the Bad Lands of Cottonwood Creek. 

 MARSUPIALIA. 

 TEIACODOISr, Marsh. 



Araer. Joiirn. Sci. Arte, 1871, July. 



This genus is placed here on the authority of Marsh. 

 Tkiacodon aculeatus, Cope. 



Proceed. Amer. Philos. Soc, 1872, p. 460, (.July 29.) 



Established on two teeth of the molar and premolar series. The mo- 

 lar is subtriaugular at the base of the crown, one side being convex: 



