EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



415 



molar type and has a rudimentary fold analogous to 

 the metastyhd. In ps (ap. 23 mm., tr. 12) still further 

 progress is made, there being 

 quite a decided antero-in- 

 ternal valley and a well- 

 defined posterior basin. In 

 P4 (ap. 24 mm., tr. 15) we 

 find a submolariform tooth 

 including a high metaconid 

 and rudimentary paraconid 

 but lacking the distinct en- 

 toconid. 



Molars . — The superior 

 molar series varies in length 

 from 118 to 131 millime- 

 ters and in addition to the 

 characters enumerated 

 above exhibits a very broad 

 and prominent antero-inter- 

 nal extension of the cingu- 

 lum, the crown of m^ being 

 broader in front (43 mm. 

 through parastyle) than it 

 is behind (32 mm. through 

 metastyle) . In some speci- 

 mens (Am. Mus. 1852) the 

 hypocone of m' rises as a 

 small but sharp and distinct 

 cusp but is not so prominent 

 as in the type of Rhadino- 

 rhinus diploconus. In other 

 specimens (Am. Mus. 1851) 

 it is less prominent and more 

 cingulate. The proportions 

 of the molars are given in 

 detail in the table (p. 416). 



The inferior molar series 

 measures 138 millimeters in 

 the female (Am. Mus. 1856). 

 A very distinctive feature is 

 the infolding of the external 

 cingulum between the outer 

 lobes of the tooth, which is, 

 however, less mai-ked in the 

 type than in most other spec- 

 imens. In the Princeton 

 type of D. Tiyognatlius 

 (Princeton Mus. 10273) the 

 only molar preserved is mg, 

 which measures (ap. by tr.) 

 64 by 25 millimeters, agree- 

 ing almost exactly with 

 specimens in the American 

 Museum. There is no proof 

 of sexual inferiority in the 



female grinding teeth (ma, ap. 62 mm., tr. 28), and 

 we should not expect it, because the females require 

 as much food as the males or more. In the type mg 



there are rudimentary folds on the inner valleys, and 

 the hypoconulid has a crenulate internal cingulum. 



Figure 353. — Lower jaws of Dolichorhinus 



A, D. valUdens, Am. Mus. 5098, one of the cotypes of " Palaeosyops " mllidens Cope, here regarded as the lectotype; Mammoth 

 Buttes, Bitter Creek, Washakie Basin, Wyo.; Washakie B?. B, D. hyognaOim, Am. Mus. 1S56; White Eiver, Uinta 

 Basin, Utah, Uinta B 2; ooronoid from Am. Mus. 1852 {Z>. Jonskeps?), White River, Uinta Basin, Utah, Uinta B 2. C, D. 

 hyogmthus, Princeton Mus. 10273 (type); White Kiver, Uinta Basin, Utah, Uinta B 2; coronoid and angle restored from 

 Am. Mus. 1852 (D. longiceps?) . A one-half natural size; B and C one-fourth natural size. 



In the more perfectly preserved mg of a female speci- 

 men (Am. Mus. 1856) the external cingulum is very 

 feebly marked except opposite the external valleys. 



