2o8 ROCHESTER ACADEMY OF SCIENCE. [April I O, 



are not regarded as true horns. The stomach is complex and the 

 caecum small. The hornless species have usually long canines. 

 Some extinct forms as OreoJon and Hyopolamus had five digits on the 

 fore foot. 



Among larger mammals, now living, this division is the most 

 numerous, and is extensively represented in the Tertiary, beginning 

 with the Eocene. The species were few in the Eocene and included no 

 ruminants. The earliest were apparently the ancestors of the Hogs, 

 and had the tubercular (bunodont) dentition, which was common iu 

 the Artiodactyla through all the Tertiary, but is now found only 

 in the Hogs and Hippopotami (non-ruminants). 



The selenodont dentition is found in the upper Eocene, but a 

 primitive or transitional form occurred in Hotnacodon, which lived in 

 the middle Eocene, having a nearly continuous series of teeth, and 

 the typical number, 44. 



The two plans of foot structure are found in the Tertiary with 

 both kinds of dentition, but no species survive with the " inadaptive " 

 plan. 



The Camels and Llamas diverged from the primitive stock in the 

 Eocene, and became in the Pliocene the most abundant of the larger 

 animals, except the Horse family. The hollow-horned ruminants 

 appeared in Europe in the Miocene, but have not been found in 

 America earlier than the Pliocene, 



The true Sheep, Goats, Giraffe, Hippopotamus, and Old World 

 Suillines [Siis, Parens, F/iacochcenis), have not been discovered in 

 America. The Suilline type, the most generalized of the Artio- 

 dactyla, and with bunodont dentition, began in America in the lower 

 Eocene, and has been abundant ever since, being now represented by 

 the Peccaries. 



Perissodactyla. These are the oldest and most abundant 

 ungulates of the Eocene, and as a group are less specialized than the 

 Artiodactyla, although the Horse, in feet and teeth, is the most 

 highly differentiated species. In all the living species the hind feet 

 have an odd number (3 or i) of toes, and the Tapir is the only one 

 with an even number (4) on the fore feet. The axis of the 

 limbs passes through the third digit. In living species there are 

 never less than twenty-two dorso-lumbar vertebrae, the femur 

 has a third trochanter, and the horns, if present, are placed on the 

 median line of the head, and are not supported on horn cores. In 

 the extinct Titanotherium there are a pair of horn cores placed trans- 

 versely. The stomach is simple and the caecum large. 



