1' A L .]-] T II K R I U M OF N E B 11 A S K A. 551 



Upon the teeth of the latter the enamel is thinner relatively upon tlie external 

 concave flices of the inner lobes of the upper molars, and the internal faces of the 

 outer lobes of the lower molars than in 0. Culbertsonii. 



ADMEASUREMENTS OF THE HEAD OF 0. GRACILIS. 



Lines. 



Estimated lengtli from the summit of the inion to the incisive alveoli, . 56 



Brcadtli at the maxillo-malur suture below the orbits, . . .29 



Breadth at infra-orbitar foramina, ••.... 12 



Estimated length of sagital crest, . . . . . .22 



Length of upper molar series, •••... 25 



" lower (' It ^ _ ^ ^ ^ . 25J- 



PALiEOTIIERIUM. Cuclcr. 

 PALyEOTIIERIUM (?) PROUTII. Oicen, Xonvood, and EransJ^^ 



(Tab. ix., figs. 3, 3 a; Tab. xii. ii, figs. 3, 4, G, 7, 8.) 



In the American Journal of Science for 1847, Dr. II. A. Prout has given a de- 

 scription of a fragment of the lower jaw of an enormous Pachyderm, suspected to be 

 a species of PakDotherium. The specimen was the hrst of the many mammalian 

 remains, which have been brought to the notice of the scientific world from the 

 vast Eocene cemetery of Nebraska. 



In Dr. Owen's collection is a fragment of the left side of a lower jaw (Tab. ix., 

 fig. 3 a), apparently of the same animal, but of a smaller individual. It is very 

 friable, and originally, i. e., after the death of the animal, was very much compressed 

 and fractured from pressure. The fragment is sixteen inches long, and contains 

 the true molars and portions of the fangs of the two preceding premolars. Along 

 the line of the true molars, the jaw measures nine and a half inches, and below the 

 last molar posteriorly is six inches in depth. 



There are also in the same collection the crown of a molar, apparently an inferior 

 third premolar (Tab. xii. b, 7), an inferior canine (8), and a fragment of an upper 

 molar (6), which I suspect belonged to the same individual as the portion of lower 

 jaw. 



Besides these the collection contains a left last lower molar (Tab. ix., 3), a right 

 lower penultimate molar, of two other individuals of the same species, and two 

 fragments of upper molars (Tab. xii. b, 3, 4), probably of the latter. The inferior 

 true molars resemble those of Palaiotherium in their form, but more particularly 

 those of Anchitherium, in having no trace of a basal ridge internally. The crowns 

 are worn upon the triturating surface into crescentic spaces, from the inner margin 

 of which the sides do not shelve downwards in a convergent manner to the base of 

 the teeth, as in PaliDotherium ; but the horns of the crescents enclose broad con- 



* Proc. Acad. Nat. Sci., v. fiC. 



