RECENT SCIENCE. 821 



these latter it is possible to find indications for an evolution which 

 must have ended in the appearance of two divisions the odd- 

 toed and the even-toed ungulates. Most laborious anatomical re- 

 searches were required for properly interpreting these rich mate- 

 rials. But the result of the work is that we already know with 

 a great approach to certitude the genealogical trees of most un- 

 gulates ; we can go back to the ancestors of the ruminants, the 

 cameloides, the chevrotains, the horses, and even to the common 

 ancestors of the whole group of ungulates ; while the genealogy 

 of other large groups of mammalia has also been worked out to 

 some extent. 



The just-mentioned discoveries in North America were soon 

 supplemented by still more remarkable finds in South America, 

 which finds follow each other with such a rapidity that anato- 

 mists will have to make strenuous efforts in order to keep pace 

 with the paleontological work. The formation which D'Orbigny 

 described as " formation guaranienne " proved to consist of marine 

 Cretaceous beds, covered by immense land deposits, which, like 

 the Laramie beds of North America, are of an intermediate age 

 between Cretaceous and Tertiary. These last beds offer an im- 

 mense interest, owing to their mammalian fossils (of much more 

 specified types than those of the Laramie), which are mixed to- 

 gether with relics of gigantic Dinosaurians, some of the latter 

 attaining lengths of more than one hundred and thirty feet. As 

 to the more recent deposits of the Argentine Republic and Pata- 

 gonia partly Eocene and partly Pliocene they are so rich in 

 mammals that more than two hundred species, some of them of 

 the most extraordinary types, have already been described by Dr. 

 F. Arneghino,* Burmeister, and Moreno ; and every number of 

 the Re vista Argentina brings some new descriptions of new fos- 

 sils both from the Argentine and Patagonia, which is now ex- 

 plored by Carl Arneghino. There are among them ungulates 

 which, to use Mr. Lydekker's words, are "totally unlike any 

 found in all the rest of the world put together," f and which com- 

 bine the characters of both the odd-toed and the even-toed ungu- 

 lates. Of them, the Macrauchenia seems to be a direct descend- 

 ant of a type which must have been a common ancestor to both 

 divisions. Another huge mammal, one of the Toxodontes, which 

 must have equaled in size the hippopotamus, also occupied an 

 intermediate position between the two groups ; while in the ear- 

 lier Tertiaries there are types which, so far as can be judged from 



* His chief works are : Los mamiferos f osiles de la America del Sud, Buenos Ayres, 

 1880; Contribucion al conocimiento de los mamiferos fosiles de la ftepublica Argentina, 2 

 parts, forming vol. vi of Actas de la Academia de Ciencias de Cordoba, Buenos Ayres, 

 1889; and several papers in Kevista Argentina de Historia Natural, Buenos Ayres, 1891. 



f Nature, vol. xlv, p. 608. 



