EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



413 



The inferior incisors are also arranged in semicircular 

 series, have obtusely pointed crowns and evenly convex 

 anterior faces, slightly recurved concave posterior 

 faces, and a pronounced median rib, which expands 

 into the basal cingulum. The transverse measure- 

 ments of the broadest part of the crown in Am. Mus. 



ap. 18 mm., tr. 15) the anterior and posterior ridges 

 are less prominent, but a large, obtuse posterior 

 basal cingulum is observed. The lower canines are 

 more obliquely placed and recurved than in T. cul- 

 tridens. There is a conspicuous antero-internal cingu- 

 lum, but the lingual side of the base of the crown is 



pglscf. 

 •p. fy. s^ 



FiGUKE 348. — Skulls of Dolichorhinus hyognathus 



Front and occipital views. One-fourth natural size. A, Am. Mus. 1851 (type of Telmatotherium cornutum Osborn), front view. B, Am. Mus. 

 1815, occipital view. Both specimens from White River, Uinta Basin, Utah; Uinta B 2. 



1856, a female, are respectively i', 14 millimeters; 

 i^, 17; i', 16. The entire breadth of these teeth in 

 this specimen is 72 millimeters. 



Canines. — The sexes are sharply distinguished by 

 the size of the lower canines : in the males the enameled 

 crown of the tusks measures vertically 41 millimeters, 



smooth in the middle basal portion only; elsewhere it 

 is cingulate. The posterior cingular ridge is slightly 

 less acute than in T. cultridens. 



In the upper canines also the difference between 

 the sexes is sharply marked, the male tusks in Am. 

 Mus. 1850 measuring (ap. by tr.) 24 by 20 millime- 



FiGURE 349. — Skull of Dolichorhinus hyognathus 



One-fourth natural size. Am. Mus 1851 (type of Telmatotherium cornutum Osborn). White Eiver, Uinta Basin, Utah, Uinta 

 B 2. X, y, Section lines in Figure 255. 



in the females only 27. The fine male tusks pre- 

 served in Am. Mus. 1850 (ap. 24 mm., tr. 21) are 

 laterally compressed, with sharply defined antero- 

 internal ridges and somewhat less prominent posterior 

 cutting ridges. No internal basal cingulum is observed 

 in this specimen. In the female tusks (No. 1856, 



ters and having a vertical height of 42, whereas the 

 female tusks of the type (Am. Mus. 1851) measure 18 

 by 15 and have an estimated crown height of 27. 



Upper premolar-molar series. — The distinctive ecto- 

 loph characters of p^-p* are a sharp vertical protocone 

 rib or ridge, a flattened to gently convex tritocone, and 



