610 GEOLOGICAL SURVEY OF THE TEEEITORIES. 



Measurements. 



M. 



Length molar series ^ 0.0:221 



Length M. 4 OOGO 



Width M 0055 



Length M. 1 0U60 



"Width M 0048 



Diameter lower incisor, transverse 0024 



Diameter lower incisor, anterior posterior 0038 



From the South Bitter Creek, Wyoming. 



Paramys undans, Marsh. 



Sciuravus undans, Marsh. Amer. Journ. Sci. Arts, 1871, (June 21.) 

 A smaller species than the P. deUcaUssinms, Leidy. The dental char- 

 acters of the mandibular series are geuerically identical with those of 

 the species of Paramys. • 



From Upper Green Eiver. 



Paramys delicatissimus, Leidy. 

 Black's Fork. 



Paramys delicatior, Leidy. 

 Cottonwood Creek and Black's Fork. 



Paramys delicatus, Leidy. 

 Black's Fork. 



PSEUDOTOMUS, Cope. 



Proceedings Amer. Philosophical Society, 1872, p. 467, (August 3.) 

 This genus is represented by the nearly complete cranium, with cast 

 of the brain-case of the typical species. The cranium is of depressed 

 form and with considerably expanded zygomata. The muzzle is broad 

 and but little elevated, so that the nasal meatus is between the alveolae 

 of the superior incisors. The frontal bone is very short, and the super- 

 ciliary margin and orbits small, and without postfrontal process. The 

 temporal fossae are large, and contract the brain-case behind the orbits 

 to a striking degree. Their anterior margins rise from the postfrontal 

 angles and converge backward, meeting in a sagittal ridge opposite 

 the anterior part of the squamosal bone. The parietal bones increase 

 rapidly in width to the squamosals, which also extend horizontally to 

 their zygomatic portion. They do not extend very far on the superior 

 aspect of the skull, nor backward beyond the auditory meatus. The 

 occipital region is concave and surrounded by a prominent crest. 



The foramen infraorbitale exterms has an inferior position, being a 

 little above the alveolar border ; it is rather small and round. There 

 is a prominent tuberosity on the under side of the basal part of the 

 molar bone, just exterior to the position of the second molar of Arc- 

 tomys ; its inferior face is truncate. The dentition is I. J-; C. f ; M. f. 

 The incisors are rather small for the size of the skull, and much as in 

 Arctomys. The inner face is truncate, the outer continuous with the 

 anterior by the lack of separating angle. The thin enamel is extended 

 part way on the outer face. At a point twice as far in front of the pre- 

 maxillo-maxillary suture as the latter is from the line of the zygoma, 

 the incisors are widely separated from each other, whence they are not 

 probably in contact when they issue from the premaxillary bones. The 



