SCIUEOMOEPHA. 819 



rior molar. The ascending ramus of the mandible originates opposite the 

 anterior part of the last inferior molar. The masseteric fossa extends to 

 opposite the anterior border of the second inferior molar. The mental fora- 

 men is near the superior border of the posterior part of the diastema. The 

 second and third superior molars, the only ones preserved, have two cross- 

 crests and a strong anterior cingulum. The external extremities of the 

 cross-crests are little elevated, and there are no other cingula. The inferior 

 molars have basin-shaped grinding faces, with a lobe at each angle. There 

 is a small tubercle between the lobes of the inner and outer pairs. The 

 incisors of both jaws are much compressed, strongly convex in front, and, 

 in the lower jaw at least, without sculpture. 



Measurements. 



u. 



LeDgth of skuU to orbit 0090 



Width between orbits 0090 



Width of muzzle 0047 



Width between last molars 0040 



Length of superior dental series 0054 



Diameters of second molar J ^'^ *'^°P*'* ^ 



c transverse OUlb 



Width of superior incisor 0013 



Length of mandibular ramus 0150 



Elevation of ramus at coronoid - 0080 



Length of diastema 0030 



Length of inferior dent.al series 0070 



Depth of ramus at second molar - 0O45 



This species is much smaller than the Sciurus vortmani, from the same 

 horizon of Oregon. The type specimen was discovered by Mr. L. S. Davis, 

 of Mr. Wortman's party. The name is given in honor of Mr. M. H. Ballou, 

 of Chicago, a naturalist and journalist, 



GYMNOPTYCHUS Cope. 



Paleontological Bulletin No. 16, p. 5 (August 20, 1873). Ann. Report U. 8. Geolog. Snrv. Terrs., 1873 



(1874), p. 476. 



Dental formula : I. - ; C. ^ ; M. -. Crowns of the superior molars sup- 

 porting two crescents on the inner side, and two cusps on the external side 

 opposite to them. Each cusp sends a transverse crest to the concavity of 

 the corresponding crescent. The adjacent horns of the crescents are united, 



