Peterson: Material Discovered in Uinta Basin. 63 



Subgenus Ischyrotomus Matthew. 21 



10. Ischyrotomus gidleyi sp. no v. 



Type: Fragment of lower jaw with My and Mt^ in place, fragment of 

 caudal. C. M. No. 3461. 



Horizon: Uinta Eocene, Base of Horizon C. 



Locality: Four miles northeast of Well No. 2, eastern end of Uinta 

 Basin. 



Characters of Type Specimens: Teeth relatively large: a well-formed 

 basin on the inner half of the molar crown with a large exit internally. 



While the type has a suggestion of Sciuravus Marsh^^ in which genus 



this type was first placed, Mr. Gidley says: "I do not think this species 



can well be referred to Sciuravus, since the proportions and general 



features of the molars are more nearly those of the 



Paramys-groxxp. It differs from the typical Paramys, 



however, in the comparatively higher tooth-crowns 



and especially in the greater development of the Fi^- 4- Ischy- 



continuous external loph, which is deeply infolded ''«''"««^ sidleyi. 



on the outer side, ... a characteristic feature of 



seum No. 3461. 



Ischyrotomus.'" The dentition in proportion to the -^ 2/1 * 



fragment is considerably larger than that of 



Sciuravus, illustrated by Matthew {I.e., p. 59). My and Mir of the 



present species each have a well-formed basin on the inner half of the 



crowns, from which extends a large internal exit, as stated above, and 



also indicated by Fig. 4. This specimen may possibly represent a new 



genus. 



Measurements. 



Vertical diameter of ramus at Mo 6.5 mm. 



Antero-posterior diameter of Mx and Mo 7 



Antero-posterior diameter of Mj 3.5 



Transverse diameter of My 3. 



Antero-posterior diameter of Mo 3.5 



Transverse diameter of Mo 3. 



21 In the Bulletin of the American Museum of Natural History, Vol. XXVIII, 

 p. 50, Dr. Matthew erected the subgenus Ischyrotomus. Mr. Gidley is of the opinion 

 that Matthew's subgenus Ischyrotomus should be given full generic rank and that 

 to it should be referred Paramys robustus and Paramys compressidens. 



* Outer side of teeth face toward the top of the page. 



^'^ Amer. Jour. Sci., Vol. II, 1871, p. 46; Ibid., Vol. XXIIIi 1907, pp. 124; 130. 

 Bull. Amer. Mus. Nat. Hist., Vol. XXVIII, 1910, p. 59. 



