868 THE JOHN DAY FAUNA. 



anterior portion extends towards the alveolus, giving an anteroposterior 

 oval on prolonged wear. Each tooth has three roots, one interior and two 

 exterior; in the first they may be described as two posterior and one an- 

 terior. The last molar is the smallest, the series exhibiting a regular gra- 

 dation in size. 



Measurements. 



No. 1. M. 



Interorbital width 0050 



Width of muzzle at middle 008O 



Depth of cranium at M. it 0138 



Length of molar series along base 0080 



Diameter of second molar f *°t^''°P°«*^"°^ '^^'^ 



( I rausverse 0020 



Width of face of superior incisor 0020 



No. 2. 



Length of cranium fiom mastoid bulla to premaxillary, inclusive 043 



Width of skull at mastoid bullie 021 



Length of superior molar series on base 008 



Width between bases of Pm. iv 0025 



John Day River region of Oregon. 



Pleueolicus leptophrys Cope. 



Bulletin U. S. Geol. Survey Terrs., IV, p. 381. American Naturalist, 1883, p. 167, fig. 16 a, b. 



Plate LXIV; figs. 7-8. 



This species is in its typical form smaller than the last, and resembles 

 in its size and its plane interorbital region the Entoptychus minor. Four 

 more or less complete crania represent it, two of which are of young and 

 two of old animals, as indicated by the degree of attrition of the molar 

 teeth. In only two of them is the parietal region so preserved as to show 

 the separate temporal ridges 



The interorbital region is flat and without superciliary ridges. The- 

 diastema is just twice as long as the series of molar teeth. The auditory 

 bulla is oval and not compressed or keeled, and the mastoid bulla is very 

 convex posteriorly, and carries a very obtuse angle from the inion above. 

 In young individuals the enamel inflection of the Pm. iv extends entirely 

 across the crown. When the internal groove has disappeared on wear, the 

 grinding surface is subround. With age the protuberance of the anterior 

 root is reached, and the form of a horizontal section of the base is pyriform. 

 The width of the front is two-thirds that of the muzzle. 



