NATURAL SCIENCES OF PHILADELPHIA. 127 



horses, which, in the absence of original specimens, afforded him the oppor- 

 tunity of making comparisons with the many equine teeth discovered in the 

 tertiary and quaternary deposits of North America. 



Prof. Owen describes a new species of Equus from South America, which 

 he names E. arcidens. From peculiarities of the teeth, he refers this species, 

 together with two others, also from South America, and named by Dr. Lund 

 E. principalis and E. neogaeus, to a genus with the name of Hippidion. From 

 some of the more important distinctive characters, viz., the extension back- 

 ward alone of the internal peninsular folds on the triturating surface of the 

 upper molars, a dozen years ago was established the genus Protohippus (Pr. A. 

 N. S. 1858, 26, with reference to fig. 1, pi. 7 of Gervais' Rech. s. 1. Mammiferea 

 Fossiles de l'Amerique meridionale). On the same grounds were also included 

 in this genus the E. principalis and E. neogaeus of Lund, together with E. mc 

 gnathus of Gervais, so far as the remains of the latter appeared to me to be 

 the equivalent of E. principalis, (Extinct Mammalia of Dakota and Nebraska, 

 &c, 1869, 276)* 



The species of equine animals referable to the genus thus far indicated are 

 as follow- : 



PROTOHIPPUS, Leidy, 1858. 

 Hippidion, Owen, 1869. 



1. Protohippus perditus 



Equus [Protohippus) perditus, Leidy : Pr. A. N. S. 1858, 26 ; Ext. Mam. Fauna 

 of Dakota, &c. 1869, 27 5, 327, 401. 



2. Protohippus arcidens. 



Equus arcidens, Owen : Phil. Tr. Roy. Soc. London, 1870, 559. 

 Equus [Hippidion) arcidens, Oweu : Ibidem, 572. 



3. Protohippus principalis. 



Equus principalis, Lund: K. Danske Vidensk. Selskab. 93, pi. xlix, fig. I. 

 Equus neogaeus, Gervais : Rech. Mammif. Fos. de l'Amer. Merid. 1855, 33, pi. 

 vii, fig. 1. 



Equus macrognathus, Gervais : Ibidem, pi. vii, fig. 1. 

 Equus (Hippidion) principalis, Owen: Phil. Tr. 572, 573. 



1. Protohippus neogaeus. 



Equus neogaeus, Lund: K. Danske Vid. Sels. 93, xlix, fig. 3. 

 Equus [Hippidion) neogaeus, Owen: Phil. Tr. 572, 573. 



5. Protohippus placidus. 



Leidy : Ext. Mam. Fauna of Dakota, &c. 277, 328, 401. 



6. Protohippus supremus. 



Leidy: Ext. Mam. Fauna of Dakota, &c. 328, 401. 



In the same Transactions appears a paper, by Prof. W. Thomson, ' on llol- 

 tenia, a 

 The genus 

 N. S. 1868, 

 tenia Carpe 

 leads me to suspect that the two are probably the same. 



November 22d. 

 Mr. J. D. Sergeant in the Chair. 

 Six members present. 



* On we 2G1 of the Ext. Mam. Fauna of Dakota and Nebraska, fig?. 2 3, have been 

 erroneously quoted instead of fig. 1 of Gervais, pi. vii, of the Rech. sur . Mammif. Foa 

 de l'Amer. Merid. 



1870.] 



