VERTEBRATA: MAMMALIA. 699 



elongated and flexible, but there would not appear to have 

 been a long proboscis. The Brontotheridcz seem to be the 

 successors of the Dinocerata of the Eocene. The chief genus 

 is Brontotherium, with which the Symbprodon and Miobas ileus 

 of Professor Cope are more or less entirely synonymous. 



The genera Titanotherium, Megacerops, and Diconodon, also 

 belong to this group. 



Fam. 5. Palceotherida. This family includes certain extinct 

 Ungulates from the Eocene and Miocene Tertiary. They are 

 characterised by the possession of three toes to all the feet, by 

 having canines, and by the fact that the lower molars have a 

 doubly crescentic form. The canines are longer than the 

 other teeth, and the dental formula is 



c*=-,pm 4=4;* 5-3 = 44- 



33 i i 44 33 



The chief genus in this family is Palaotherium itself. Several 

 species of this genus are known, varying in size from a sheep 



Fig. 394. Grinding-surface of the molar and praemolar teeth of the upper jaw of 

 Palceotherium crassum. (After Owen.) 



up to a horse. From the form and size of the nasal bones it 

 is deduced, with great probability, that the Palceotheridce pos- 

 sessed a short movable proboscis or trunk. 



Fam. 6. Macrauchenida. This family comprises the single 

 genus Macrauchenia from the late Tertiary deposits of South 

 America. The animals included in this genus were of large 

 size, with three-toed feet, and a third trochanter to the femur, 

 but having cervical vertebrae of the type of those of the Came- 

 lidce. The general form of the skull is horse-like, and the in- 

 cisors have a coronal pit. The teeth form nearly a continu- 

 ous series, and the dental formula is 



i 3lZl . c I ZZ I ; p m 5^5 . m 3n3 = 4 6. 

 33 i i 44 33 



Fam. 7. Solidungula or Equida. This family comprises the 

 Horses, Asses, and Zebras, characterised by the fact that the 

 feet, in living forms, have only a single perfect toe each, en- 

 closed in a single broad hoof, without supplementary hoofs 



