304 



F. B. Loomis — Osteology and Affinities 



a moderate diastema which precedes the reduced two-rooted 

 first premolar, while behind this tooth a much greater diastema 

 occurs, separating it widely from the second premolar, which, 

 like its predecessor, is reduced and two-rooted. The third pre- 

 molar follows without any diastema, and is a narrow elongated 

 tooth, but with none of the specializations of the teeth which 

 follow it. The fourth premolar has acquired the selenodont 

 character, though but single-lobed, its inner and outer cusps 

 having developed into high crescentric ridges, with a deep pit 

 between. The three molars are all extremely hypsodont, 



Fig. 4. 



Fig. 4. Stenomylus hitchcocki, upper dentition and palate, x 1/2. 



which is one of the most marked features of the genus. Each 

 tooth is very simple, consisting of two lobes, each with a deep 

 pit in it. There is no cement in the valleys. Each tooth is 

 nearly flat on the outer side, there being but a slight convexity 

 outside the paracone and metacone, and no column except that 

 the anterior border of each molar is developed into a parastyle. 

 The widest portion of the series is at the second lobe of the 

 first molar. The crown of each molar is greatly developed in 

 height, as is seen in the section of a second molar (fig. 5), the 

 top being slightly narrower than the base, so that as they wear 

 the teeth appear relatively wider. A slightly worn second 



upper molar of S. hitchcocki has a 

 crown 23 mm high which contained a 

 pit 19 mra deep, these pits in the upper 

 molars being materially deeper than 

 in the lower molars. The successive 

 molars seem to come up slowly or 

 else the wear is very rapid, for when 

 molar 3 is but slightly worn the first 

 molar is down to the bottom of the 

 pit. In addition to the considerable 



Fig. 5. 



molar, to show depth of pit 

 xl/1 



Fig. 5. Stenomylus hitch- 

 cocki, section of upper second height of the crown the upper part 



of the pulp cavity fills m with dent- 

 ine, so that some time after the bot- 

 tom of the pit is reached the tooth still has a solid center, in 

 the middle of which is a small discolored " mark." Inasmuch 

 as the wear seems to continue considerablv below the base of 



