818 THE JOHN DAY FAUNA. 



verse section, and the enamel is perfectly smooth. The inner angle is 

 sharp, and the enamel does not pass it, but the external angle is rounded, 

 and the enamel covers it, narrowly overlapping the side of the tooth. 



The molars exhibit the basin-shaped character, with the tubercles mar- 

 ginal, as usual in Sciurus. They increase regularly in size from the front 

 backward. The transverse crests are marginal, and terminate in cusps at 

 the inner extremity, which are separated by a lower acute median cusp. 



A longitudinal crest connects the crests just within their outer extremi- 

 ties; it exhibits a loop dii-ected outward. A low ridge passes from the pos- 

 terior outer butress, just in front of the posterior margin, in the last two 

 molars. Anterior cusps of first molar contiguous. 



Measurements. 



M. 



LeDgth of ramus to end ofM. 4 0120 



Length of molars 0088 



Length of third molar 0015 



Width of third molar 0018 



Depth of ramus at third molar 0050 



Width of incisor 0015 



As compared with the corresponding part of the Sciurus hudsonius, the- 

 best preserved ramus of this species differs in the more robust incisor teeth, 

 in the less anterior extension of the masseteric fossa, and in the rather 

 smaller size. 



Sciurus ballovianus Cope. 



Bulletin U. S. Gelog. Surv. Terrs., VI, 177, February 11, 1881. 

 Plate LXIII; figs. 5-6. 



This squirrel is the second species of its genus supposed to occur in the 

 John Day beds of Oregon, and the third Sciurus obtained thus far from the 

 Lower Miocene or Oligocene of the West. The typical specimen fortunately 

 includes the cranium, with both rami of the mandible, so that its reference 

 to the genus Sciurus rather than to Gymnoptychus is assured. Like tlie latter 

 genus, the infraorbital foramen is reduced to a slit, but, unlike it, there is 

 but one internal tubercle of the crowns of the superior molars instead of two. 



The skull is flat above, and the interorbital space is also flat, and is 

 remarkably wide. Temporal ridges none. Muzzle short and narrow. 

 Palate wide, its posterior notch extending as far forwards as the last supe- 



