DAKOTA AND NEBRASKA. 207 



large species of Palceotho-ium, The specimen was the first of the mammalian fossils 

 brought to the knowledge of naturalists from the great cemeteries of Dakota and 

 Nebraska. 



Besides the specimen described by Dr. Prout, I have had the opportunity of 

 examining many othei's derived from the same locality, in collections subsequently 

 made by different explorers. The specimens consist of fragments of jaws with teeth, 

 isolated teeth and fragments of others, together with portions of bones of other parts 

 of the skeleton. They are usually much fractured, and are pervaded by fissures in 

 all directions, the result of pressure whilst imbedded in the strata to which they be- 

 long. The fragments are generally retained in their original position, cemented 

 together by portions of the imbedding matrix, or they are but slightly displaced. If 

 it were not for this coherence of the fragments, the specimens would be crumbled 

 into a multitude of particles. 



The most characteristic specimen of Titanotherium Prouti I have had the opportu- 

 nity of inspecting consists of alveolar portions of the upper jaw, including the inter- 

 maxillaries, and containing nearly all the molar teeth, with the sockets of the others. 

 It was obtained, together with several additional molars, a fragment of a lower jaw, 

 and portions of other bones, by Messrs. Meek and Hayden, and belongs to the 

 collection of Prof James Hall, of Albany, N. Y., by whom it was loaned to me for 

 examination. A complete series of the molar teeth, as restored from the two sides, 

 together with the fore part of the jaw, is represented in figures 1, 2, plate XXIV, 

 three-fourths the size of nature. 



Other important specimens consist of portions of lower jaws with teeth, previously 

 described in the Ancient Fauna of Nebraska, and a number of isolated molar teeth 

 since obtained by Drs. Hayden and Evans. 



The corresponding teeth from different individuals vary considerably in size and in 

 the degree of development of a basal ridge. The variation is probably due to a differ- 

 ence in sex, — the more robust belonging to the male, the others to the female. 



The formula of dentition of Titanotherium can be ascertained with certainty from 

 the different fossil specimens, except as concerns the number of inferior incisors. The 

 upper jaw specimen of Prof Hall's collection, above mentioned, indicates the follow- 

 ing series : 



In. 2—2, c. 1—1, p. m. 4—4, m. 3—3 = 20. 



Fragments of lower jaws exhibit the same number of molar and canine teeth, and 

 probably there existed also the same number of incisors as in the upper jaw. 



The upper molar teeth form a continuous row, successively increasing in size from 

 first to last. The true molars are constituted alike after the same pattern, and they 

 are related in position with one another as in PalcBotherium, Anoplotherium, Rhinoceros 

 and the ruminants. The outer sides ai"e oblique, with the antero-cxterual border pro- 



