816 THE JOHiSr DAY FAUNA. 



None of this species of this fauna are of larger size than their modern 

 representatives. In the cases of the beaver, squirrels, and rabbits, the an- 

 cient species are the smaller. 



SCIUROMORPHA. 



SCIURUS Linn. 



In this genus the molars are f or \, the first superior small when pres- 

 ent. The grinding surfaces of the crowns when unworn present in the 

 superior series a single internal cusjJ, which is low and anteroposterior. 

 From this there extend to the external border of the crown two low trans- 

 verse ridges, whose exterior terminations are somewhat enlarged. In the 

 lower jaw the transverse ridges are not visible, and there is a low tubercle 

 at each angle of the crown, between Avhich there may be others on the 

 border of the crown. Attrition gives the grinding surface of the latter a 

 basin-like character. The foramen infraorhitale is a short, narrow fissure, 

 situated in the inferior jiart of the maxillary bone in front of its tooth-bear- 

 ing portion, but descending nearly to the level of the alveolar border. 



The well-known characters of this genus are found in the mandibles of 

 species which I obtained from the White River Miocene beds of Colorado 

 and Oregon. The teeth display the subquadrate form of this genus, witli- 

 out any tendency to the transverse enlargement seen in Ardomys, Cynomys, 

 and Spermophilus. Two of the species, 8. vortmani and S. relidus, are as 

 large as our gray and red squirrels, respectively, and the third, S. baUoviamis, 

 is about the size of the Tamias quadrivittatus. 



SciURUS V0RTMA.NI CopC. 



Paleontological Bulletin No. 31, p. 1, December 24, 1879. Proceed. Amer. Pliilos. Soc, 1879, p. 370. 



Plate LXIII; fig. 4. 



Like the S. relidus of the Colorado White River beds, this is a rare 

 species, being only represented by a mandibular ramus in my collection. 

 This part is remarkable for its depth as compared with its length, and the 

 base of the coronoid process has an anterior position. It rises opposite the 

 posterior part of the third molar, and its anterior border descends to a point 

 just below the posterior part of the first molar. The inferior border of th& 



