OF THE WHITE RIVER BEDS OF MONTANA. 



271 



The canine is narrow laterally, more nearly flat on the inner surface and divided 

 into three convexities by two faint longitudinal furrows. The outer surface is more con- 

 vex, divided in the same way, but the middle convexity is much greater. The tooth con- 

 tracts uniformly anteriorly, exteriorly and posteriorly from the base upward, ending in a 

 small, smooth, rounded point. The appearance of the enamel is like that on the rest of 

 the teeth, in all of which the inner angles and sometimes the outer are smooth, the other 

 inner surfaces less so; while on the outer surfaces the enamel is slightly crinkled. The 

 height of the crown was about .035 ni. 



The first premolar is small, longer antero-posteriorly than the incisor, and is thin — 

 the thickest part and the apex being slightly anterior to the middle. The forward slope 

 of the edge from the apex is straight, but back of the apex it drops abruptly, then slopes 

 backward and curves downward. The thin anterior part, as in the incisor, projects a, 

 little anteriorly to the root, There is a short cingulum on the posterior inner side, which 

 continues as a faint ridge to the anterior edge of the tooth. 



Premolar 2 is longer antero-posteriorly and much higher, having a high, narrow 

 apex, which is nearly central. From this apex the edges descend, vertically anteriorly 

 and nearly so posteriorly for a short distance, and then both slope away, though not with 

 exact symmetry, to the anterior and posterior edges of the tooth at the base of the crown. 

 The outer convexity is not straight vertically. Beginning at the apex it extends down- 

 ward a short distance, and then curves forward. The inner convexity is straight and 

 median. There is an outer cingulum. The inner cingulum begins at the anterior angle 

 of the tooth, but the posterior part is broken away. 



The third premolar is nearly an enlarged copy of P 2 . It is larger in every way. 

 The main cusp is rather narrow, but the enlargement and expansion of the cingulum on 

 the posterior inner part of the tooth gives the base a triangular form, with the posterior 

 inner angle rounded. The cingulum encloses a large concavity or an oblong cup-like 

 depression. A second premolar of a young Hyopotamm in the Princeton Collection (No. 

 10652) resembles this tooth. 



P 4 has an outer and an inner crescent, the outer being the larger, longer and higher. 

 There is an anterior and a posterior outer buttress at the outer angles. Both the ante- 

 rior and posterior cingula are large and enclose furrows between them and the crescents. 

 The outer crescent is concave externally with a median convexity. This is also true of 

 the inner crescent. The posterior faces of the crescents are in the same plane. The 

 anterior horn of the internal crescent is convex on the anterior face, and abuts against a 

 small but comparatively high corneal cusp or style which partly interrupts the valley 

 between the two crescents. 



