GEOLOGICAL SURVEY OF THE TERRITORIES. 357 



TriacodoNj Harsh. 



Triacodon fallax 



Is tlie name given to another insectivorous mammal, by Prof. Marsh, 

 from some remains found at Grizzly Buttes, Wyoming. 



EODENTIA. 



Judging from the number of fossils already found, the gnawing 

 animals were abundant in the Bridger Tertiary fauna. None of them, 

 thus far indicated, were remarkable for size, in comparison with those 

 now living. 



Paramys. 



A genus apparently allied with that to which the Maryland Marmot 

 belongs, and indicated by three portions of lower jaws belonging to as 

 many distinct species. The specimens were discovered the last summer, 

 in the vicinity of Fort Bridger, by Dr. Carter, and by him transmitted 

 to the writer. The animals were no doubt powerful' gnawers, as the 

 incisor teeth are observed to extend far back in the jaw, not only be- 

 neath but also behind the grinders, as in the Beaver. The jaws are 

 comparatively short and deep. The ridge defining the muscular fossa 

 on the outer back x^art of the jaw is strongly pronounced, indicating 

 powerful masticatory muscles. The molar teeth are four in number, 

 and have a distinct enameled crown inserted by fangs, as in the squir- 

 rels and marmots. The triturating surface of the crowns is bounded 

 by prominent angles, inclosing a cup-like hollow. The species are as 

 follows : 



Paramys delicatus. 



The largest one, about one-fourth less than the Maryland Marmot. 

 Length of the molar series of teeth, f of an inch. Diameter of the inci- 

 sors, 2 J lines fore and aft and IJ lines transversely. 



Paramys delicatior. 



The second- sized species. The molar series is 7^ lines long. The 

 incisors are 2 lines fore and aft and IJ in transverse diameter. 



Paramys delicatissimus. 



The smallest species. Length of the molar series, J inch. Diameter 

 of the incisors, 1 J lines fore and aft and 1 line transversely. 



Mysops. 



Mysops minimus. 



A smaller rodent than any of the preceding, and not much larger 

 than the Domestic Mouse, is indicated by a ramus of the lower law re- 

 taining a pair of molar teeth. The construction of the jaw and the 

 number of grinders are the same as in Paramys, but the teeth present a 

 different arrangement of the sculpturing of the crown. The penultimate 

 molar in its worn condition presents a pair of transverse ellipses 

 of dentine united by a median isthmus of the same substance and 

 bordered with enamel. The crown of the last mohir exhibits five 

 shallow tubercles, with minute exposed islets of dentine at their summit. 

 The length of the entire molar series is ^ inch. 



