Peterson: Material Discovered in Uinta Basin. 65 



Measurements. 



Total antero-posterior diameter of P^ and M- 5 mm. 



Antero-posterior diameter of P^ 2 " 



Transverse diameter of P- 2.3 " 



Transverse diameter of M- 3.4 " 



Antero-posterior diameter of M' 2.3 " 



Genus Prosciurus (?) Matthew.-^ 



12. Prosciurus (?) robustus sp. nov. 



Fragments of lower jaws of two individuals: C. M. Nos. 2925 and 

 2926 from Horizon C of the Uinta, six miles east of Myton, Utah, are 

 here provisionally referred to Matthew's genus of the lower Oligocene, 

 see Fig. 6. 



In a note from Mr. Gidley, dated January 20, 1916, he says: "There 

 are some peculiarities about the two forms I have provisionally re- 

 ferred to Prosciurus which indicate that better material may justify 

 making a new genus for these species. "^^ 



Unfortunately there are no lower teeth with the type of Proscmnis, 

 and consequently no basis of comparison except size. The present 

 specimens appear to be at least twice the size of Prosciurus vetustus 

 Matthew. To place the specimens with the latter species would seem 

 to be out of the question. On the basis of its large size and the geologi- 

 cal horizon in which it is found, the name Prosciurus (?) robustus sp. 

 nov. may be proposed: No. 2925 is the type and No. 2926 is the 

 paratype. This is mainly in order to have all the rodents from the 

 Uinta more completely recorded. 



M EASUREMENTS. 



Type Paratype 

 No. 2925. No. 2926. 



Antero-posterior diameter of M 2 6 mm. 



Transverse diameter of M^ 4 mm. 



Antero-posterior diameter of M3 7 mm. 



Transverse diameter fo M3 5 mm. 



23 Bull. Amer. Mus. Nat. Hist., Vol. XIX, 1903, p. 213. 



2^ In a later communication Mr. Gidley says that he thinks that it is possible 

 that the species they represent may after all have been derived from the Leptotomiis 

 group of Paramys. This cannot be determined, however, until the upper teeth 

 are known. 



5 — DEC. 2, 1919. 



