III.] PYROTHERIUM. 85 



members of the rodent order, to have had their toes protected 

 by nails. Like as are these animals to rodents, the resemblance 

 to that group is carried to a still greater extent in certain small 

 forms from the Santa Cruz beds which have been named Pachy- 

 ruchus and Hegetot her turn ; these constituting a third family, the 

 Pachyruchida. From the features referred to, the reader might 

 be disposed to consider that there is some direct genetic affinity 

 between rodents and the group under consideration, but this is 

 clearly not the case, such resemblances as exist being solely the 

 result of that parallelism in development which appears to have 

 been such an important factor in the evolution of mammals. 



It may be well to mention here that in a recent paper 1 Dr 

 Noack suggests an intimate affinity between the toxodonts and 

 the existing hyraces (Hyracoidea) of Africa and Syria; adding 

 that the presumed affinity affords evidence of a land-connection 

 between Africa and South America. The two groups are, however, 

 essentially different in regard to the structure of the fore-foot, in 

 which the bones of the carpus or wrist are arranged, as already 

 shown, in the alternating manner among the toxodonts, whereas 

 in the Hyracoidea they form a linear series. Moreover, the molar 

 teeth of the two groups are markedly distinct, although in both 

 they approximate to the perissodactyle type. Still there is a pos- 

 sibility that the Hyracoidea may represent a less specialised branch 

 which has originated from the primitive toxodont stock, but has 

 retained the linear type of carpus ; and if this really be the case, 

 it would afford very strong confirmation of the view that South 

 America received its earliest ungulates by way of Africa and the 

 Antarctic Continent. 



A remarkable ungulate from the Patagonian beds, with molar 

 teeth very like those of the extinct European genus 

 Dinotherium, and bearing a pair of large tusks in 

 the lower jaw at least, has been tentatively assigned by the present 

 writer to the Proboscidea ; but judging from the distinction of the 

 other ungulates of the older Argentine Tertiaries from those of 

 the rest of the world, it is more probable that it represents a 

 sub-order by itself. Pyrotherium, as the animal is called, was 



1 ZooLJahrb.-AbtheilfurSystemat. vol. vil. pp. 540 542. 



