IV. 



The La Plata Museum. 



{Continued from page 35.) 



THE above are some of the most noteworthy of the fossil mammals 

 in the La Plata Museum from the Pampean beds and the some- 

 what older deposits of the Parana and Monte Hermoso; and I now 

 pass on to the consideration of a few of the more interesting types 

 from the still older Patagonian beds. Putting aside the Edentates, 

 which 1 had no time to examine in detail, my observations will be in 

 the main confined to the Ungulates, of which I made a special study. 

 The most abundant, and at the same time one of the most interesting, 

 of these early hoofed mammals is the one to which Owen applied 

 the name of Nesodon, this genus being represented in the Museum by 

 a vast series of remains, including many perfect skulls, as well as 

 jaws, teeth, and limb-bones. Allied in many respects to Toxodon, 

 these Ungulates differed by the closer approximation of their cheek- 

 teeth to the Perissodactyle type of structure ; the name of the genus 

 being derived from a well-marked island-like lobe found on the inner 

 side of the upper molars. There are likewise important differences 

 in the conformation of the cutting-teeth, and also in the structure of 

 the skeleton in general, which in many respects is much less 

 specialised than that of the allied Pampean genus. Moreover, all 

 the three species of Nesodon which I can alone recognise, were vastly 

 inferior in size to the gigantic Toxodon, the smallest of the three 

 being not much larger than a, sheep. Hitherto, not much attention 

 has been paid to the limb-bones of this genus; but I have been 

 fortunate enough to identify not only the "long" bones, but likewise 

 the calcaneum and astragalus, and thus to confirm the presumed close 

 relationship of Nesodon to Toxodon.^ 



As our palaeontological readers are probably aware, Owen 

 described two species of the genus Nesodon, together with a third one 

 which has been subsequently ascertained to belong to a totally 

 different type of Ungulate. One of these two species {N. imhricatus) 

 was an animal approaching the dimensions of a small rhinoceros, 

 while the second {N . ovinns) was, as already said, not very greatly 

 larger than a sheep. Between these two extremes I find an 



1 Some of these bones are described and figured in the forthcoming issue of the 

 An. Mus. La Plata, containing an account of the results of my own work. 



