136 



University of California Publications. 



[Geology 



Cranium. — Anterior to the orbit the facial region is abruptly 

 contracted both laterally and vertically. This feature is peculiar 

 to T. deCedens. In the remaining species the facial region is of 

 the elongated type of T. osmonti (PL 17). Between the orbits, 

 the forehead is convex, without elevated superciliary borders. A 

 pair of broad grooves diverging anteriorly extend forward from 

 the supraorbital foramina. They are separated by a low 

 ridge. The median ridge and the grooves are minor features 

 and do not materially affect the general convexity of the fore- 

 head. The palate is flat. There is but little downward curvature 

 of the premaxillae, in striking contrast with T. osmonti and Dico- 

 tyles. The premaxillary border of the anterior nares has been 

 fractured on either side and is restored in the figure. 



Mandible. — Portions of both rami are preserved with cra- 

 nium No. 1989. The left ramus represented in Plate 16 is the 

 better preserved. It increases in depth posteriorly. There are 

 four mental formina observable, one slightly posterior to P 3 , 

 two beneath P 4 and one beneath the anterior half of M x . 



Dentition. — The crowns of the first pair of superior mcisors 

 are not preserved in either specimen. The second pair resemble 

 the corresponding teeth in Dicotyles. The third pair, preserved 

 in cranium No. 1989, are long and pointed and considerably 

 recurved. The canines are broad blades, triangular in cross- 

 section with the apex of the triangle directed posteriorly. The 

 outer face is marked by two ridges, the posterior much stronger 

 than the interior. P 1 is double rooted and is situated on the 

 inner side of the base of the canine. In the figure, it is repre- 

 sented as having slipped from the alveolus. As preserved, the 

 extension of this tooth below the alveolar border does not exceed 

 the length of P L '. P 2 is like the first, but larger. P 3 carries a 

 large postero-internal basin-shaped heel. In addition to proto- 

 eone and deuterocone, the tritocone is more or less developed in 

 P*. There are short diastemata anterior and posterior to P 1 , 

 but the rest of the superior dentition is in close series. The 

 molars increase rapidly in diameter posteriorly. The enamel of 

 the crowns is mammilated especially in M 3 . A large antero- 

 internal style is present on this tooth and also a prominent pos- 

 tero-internal heel, the surface of which supports a number of 



