122 NATURAL SCIENCE. Feb.. 



solely characteristic of the Camel family. Like the other suborders of 

 extinct Ungulates peculiar to South America, the Litopterna further 

 diflfer from both the Artiodactyla and Perissodactyla in having the 

 bodies of the cervical vertebrae articulating together by flat terminal 

 surfaces, instead of by a ball-and-socket joint. They likewise pre- 

 sent the same strongly-marked similarity to the Perissodactyla in the 

 structure of their cheek-teeth — a feature doubtless inherited from a 

 common ancestor among the Condylarthrous Ungulates of the 

 Eocene, but more or less specially developed subsequently by paral- 

 lelism. The Litopterna are divisible into the two families of the 

 Macraucheniidae and Proterotheriidae, the former being distinguished by 

 the full and uninterrupted dentition; while in the latter the teeth are 

 reduced in number and interrupted. An ancestral form of Macran- 

 chenia is represented by the species of Oxyodontotheriiiin (Theosodon) of 

 the Patagonian Tertiaries, which were much smaller creatures than 

 the Pampean animals, while an intermediate type existed in the 

 Parana beds. 3 In this family, as well as in the next, I have again to 

 deplore a superabundance of names, both specific and generic, as I 

 have pointed out in the memoir referred to. 



Among all these curious types of Ungulates, none are more 

 remarkable than the Proterotheriidae, as represented by the genera 

 Protevotherium and Diadiaphorus of the Patagonian Tertiaries and the 

 Parana beds. These were animals varying in size from a peccari to 

 a tapir, with molar teeth more or less closely resembling those of 

 the European Oligocene genus PalcBothermm, but having only a single 

 pair of tusk-like incisors in the upper jaw, and two pairs of lower 

 incisors, one of which was much larger than the other. From the 

 researches of Senor Ameghino, it is already known that in one 

 member of this family [Epitherinni), occurring in beds above the 

 horizon of the Patagonian deposits, the feet were of the general type 

 of those of Hippavion — that is to say, the middle toe was greatly 

 developed at the expense of the two lateral ones, which were small 

 and functionless. I find, however, from the evidence of the speci- 

 mens in the La Plata Museum, that some at least of the Patagonian 

 representatives of the family were likewise provided with feet of the 

 same highly-specialised type, while I have no evidence that any of 

 them had functional lateral digits. 



This extreme specialisation of the feet of these otherwise 

 generalised Ungulates is a feature interesting enough in itself, but it 

 is of still more importance in regard to the relative age of the strata 

 in which their remains occur. The Patagonian Tertiaries of Santa 

 Cruz, from which the remains of Proterotheriidae are obtained, appear 

 to be nearly, if not quite, the oldest South American deposits yielding 

 remains of land mammals. They are correlated by Sehor Ameghino 

 (who, by the way, suggests that Protevotherium and Diadiaphorus were 



3 For this form Senor Ameghino has proposed the barbarous name Scalabyhii- 

 therium, a term which may be changed to Sculabrlnia. 



