1856.] 59 



Notices of some-remains of extinct Mammalia, recently discovered by Dr. F. V. Hay den 



in the bad lands of Nebraska. ) 



By Joseph Leidy, M. D. 



1. HiPPARION OCCIDENTALE, Lcidj. 



This second American species oi Hipparion is established on specimens of five 

 superior and one inferior molar teeth, discovered by Dr. Hayden, on the White 

 River of Nebraska. The internal isolated enamel column of the upper molars, 

 on the worn crown, is elliptical and more than twice the length of the breadth. 

 The central columns of the same teeth are comparatively moderately folded. 

 Antero-posterior diameter of the first upper molar 15 lines, transverse diameter 

 lOJ lines ; antero-posterior diameter of the largest of the back upper molars 13 

 lines; transverse diameter 12 lines; smallest of the back upper molars 11 lines 

 square. Antero-posterior diameter of the back inferior molar 12 lines, trans- 

 verse diameter Vi lines. 



2. Hyopotamus americanus, Leidy. 



This species is founded upon a number of specimens of molar teeth, which 

 were discovered by Dr. Hayden, in company with remains of Titanoiherium, in 

 Nebraska Territory. The teeth indicate a species of the same size as Hyopotamus 

 bovinus, Owen. Among the specimens are the posterior two upper molars of both 

 sides of the jaw from the same individual ; and they present almost a repetition 

 of form of the homologous pair of H. vectianus, Owen. The collection also con- 

 tains two premolars in conjunction, apparently from the same individual as the 

 true molar just mentioned. They correspond to the second and third premolars 

 of Anthracotherium : the crown of the second premolar consisting of a single 

 large trihedral lobe, with a tubercle at its postero-internal basal angle ; and the 

 crown of the third premolar being formed of a transverse pair of lobes, of which 

 the outer one is trihedral and the inner one is smaller and conical. These pre- 

 molars undoubtedly belong to the permanent dentition, and if they are not the 

 second and third of the series, they are certainly the latter and the fourth. In 

 either case, they confirm an opinion formerly expressed (Anc. Fauna of Nebraska, 

 p. 45,) that the teeth represented by Prof. Owen, as the third and fourth per- 

 manent premolars of Hyopotamus vectianus, (Lond. Quart. Journ. of the Geol. 

 Soc, pi. vii, vol. iv,) really belong to the deciduous dentition ; and, therefore, 

 although Hyopotamus may not be identical with Anthracotherimn, it is much more 

 nearly allied to it than was suspected by its distinguished author. 



The. measurements of some of the molar teeth of Hyopotamus americanus are 

 as follows : 



Antero-posterior diameter of the superior last true molar, externally, 13J lines. 

 Transverse do. do. do. anteriorly, 15 do. 



Antero-posterior diameter of the superior third premolar, 6 do. 



Transverse do. do. do. 8| do. 



Antero-posterior diameter of the superior second premolar, lOj do. 



Transverse do. do. do. 8| do. 



Mr. Vaux, on behalf of the Publication Committee, presented the 

 Annual Report, which waa adopted. 



ELECTION. 



Mr. William P. Blake, of Washington, D. C, and B. A. Hoopes, 

 Esq., of Eagle Harbor, Michigan, were elected Correspondents. 



