THE MAMMALIA. 43 



genera, PaleocJmrus and Choirothermm^ had already the dentition 

 of the pig species, but still had the full number of functional toes. 

 The hogs and peccaries, though so nearly allied, have two distinct 

 lines of pedigree. America possessed a line of pig-shaped ani- 

 mals, which may be traced up from the Eocene Eohyus up to the 

 modern peccary. Immense numbers of collateral branches were 

 thrown out, some attaining the size of a hippopotamus. In speak- 

 ing of Eohyus of the Lower Eocene of North America, Professor 

 Marsh observes : — " In every vigorous primitive type which was 

 destined to survive many geological changes, there seems to have 

 been a tendency to throw off lateral branches, which became 

 highly specialised and soon died out, because they were unable to 

 adapt themselves to new conditions. The narrow path of the 

 persistent Suilline type, throughout the whole Tertiary, is strewn 

 with the remains of such ambitious offshoots ; while the typical 

 pig, with an obstinacy never lost, has held on in spite of catas- 

 trophes and evolution, and still lives at the present day. In the 

 Lower Eocene, we have the genus Parahyus, apparently one of 

 these short-lived specialised branches. It attained a much greater 

 size than the true lineal forms, and the number of its teeth was 

 much reduced. In the Middle Eocene we have on, or near, the 

 true line, Helohyus. All these early Suillines, with the possible 

 exception of Pai'ahyiis, appear to have had at least four toes, all 

 of useable size. In the Lower Miocene, we find the genus 

 Perchcerus^ seemingly a true Suilline, and with it remains of a 

 larger form, Elotherhim, are abundant. Elotheriiiin lived both in 

 America and Europe. It affords another example of the Suilline 

 offshoots already mentioned. Some of the species were nearly 

 as large as a rhinoceros, and in all there were but tivo serviceable 

 toes, the outer digits seen in the modern pig being represented 

 only by small rudiments concealed beneath the skin." 



Enormous numbers of transitional forms existed also in the 

 three Tertiary periods, presenting characteristics both of the pigs 

 and the ruminants. Of these, one of the most curious was the 

 family of the A7ioplotheridce. Anoplotheriwn of the Eocene was 

 about the size and shape of an ass. It possessed a long-pointed 

 tail. Its molar teeth resemble, in some respects, those of the 

 rhinoceros, and its dentition is peculiarly primitive, as it pos- 



