260 ON THE EXTINCT MAMMALIA OF 



Equm Americanus. The same author, in his Recherches sur les Mammiferes Fossiles 

 de I'Amerique Meridionale, page 33, plate vii, 1855, describes and figures a number 

 of equine remains which he refers to two species, under the names of Equus neogcms 

 and Equus Devillei. 



Under the head of Equus neogoeus M. Gervais places E. principalis, Lund; E. 

 macrognathus, Weddell ; E. Americanus, Gervais ; and E. curvidens, Owen. Under 

 the head of Equus Devillei he places E. pirincipalis with a note of interrogation, and 

 he observes " that slight differences in the form of the lower molars and a less size 

 are the only characters that can yet be assigned to distinguish it from E. neogceus." 



In the upper molar teeth of Equus principalis and E. neogceus, as represented by 

 Dr. Lund in the work above mentioned, the central lakes of the worn triturating 

 surface are comparatively of extreme simplicity. The internal median fold of 

 enamel, from its isthmus of connection with the antero-median column of the tooth, 

 is reflected backward only, and it forms a short ellipse. In E. principalis this ellipse, 

 as is also the case with that formed by the enamel fold just behind, is oblique ; in E. 

 neogcetis the corresponding ellipses have their long diameter antero-posterior, which 

 difference is favor of the distinction of the two species. 



In comparing M. Gervais' figure 1, plate vii, of the work above mentioned, repre- 

 senting the posterior four upper molars much worn, and which are referred by the 

 author to E. neogceus or E. macrognathus, they will be observed in the characters 

 above stated to agree with the tooth of E. principalis as represented by Dr. Lund. 



In the upper molar of E. curvidens, as represented by Prof Owen, the internal 

 median fold of the triturating surface is reflected forward as well as backward of its 

 isthmus, forming a comparatively long ellipse with the long diameter antero-posterior. 

 The same arrangement exists in the upper molars of the recent Horse, except in the 

 first one and in those of the temporary series. No extent of wearing in the teeth of 

 this animal will give rise to such an appearance of the internal median fold as that 

 represented in M. Gervais' figure just mentioned, so that the difference is not one 

 of age. 



The two isolated upper molars represented in M. Gervais' figures 2, 3, plate vii, 

 likewise referred to Equus neogceus or E. macrognathus, agree in the arrangement of 

 the internal median fold of the triturating surface with E. curvidens, Owen, but the 

 enamel enclosing the central lakes is rather more complexly folded. 



From an examination of the figures and the descriptions of the fossil upper molar 

 teeth above mentioned, I am led to suspect their reference to species as follows : 



1. Equus curvidens, Owen : Zool. Voy. Beagle, pi. xxxii, figs. 13, 14. E. neogceus or 



E. macrognathus. Gervais : Rech. Mam. Fos. Am. Merid. pi. vii, figs. 2, 3. 



2. Equus neog^us. Lund : Dansk. Viden. Selsk. Afh. xii, pi. xlix, fig. 3. 



