MAMMALIA, 17 



FAMILY LOPHIODONTIDiE. " 



Coj)e emimerates fifty species in the Lophiodontidce, all from the 

 Eocene of America and Europe. They vary in size from that of a 

 Rabbit to that of an Ox, and resemble most, among living animals, 

 the Tapirs. 



No. 25. [105] Pliolophus VUlpicepS, Owen. 



Skull and Lower Jaw (cast). This odd- 

 toed, hoofed herbivore, stood intermediate 

 between the Tapir and Palteothermm, and has 

 some affinities to the Hog and Horse. The 

 dentition is like that of nearly all Eocene 

 quadrupeds, atype not exhibited by any later (?) 

 or existing mammal, namely: three incisors, 

 one canine, four premolars, and three molars in each ramus. Six species of 

 this genus are known, five of them being from the American deposits. This 

 interesting fossil was discovered in the London Clay (Eocene), of England, and 

 is now in the British Museum. 



SECTION B-ARTIODACTYLA. 



In this section the digits are four or two in number, and the axis 

 of the limb passes between the third and fourth, which make a sym- 

 metrical pair, and by their compressed form have suggested the term 

 " cloven-footed." The femur has no third trochanter. The dorsa- 

 lumbar vertebrae are usually nineteen. The true horns are in trans- 

 verse pairs, with osseous " horn-cores." The antlers of the Cervidce 

 are themselves osseous, and deciduous, and are not regarded as 

 " true horns." The stomach is complex and the csecum small. The 

 hornless species have usually long canines. 



Among larger mammals, now living, this section is the most num- 

 erous, 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, as the Eohyus and Helohyus, and they had the tubercular 

 (bunodont) dentition, which was common in 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 Homacodon, which lived 

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

 the typical number, 44. Eomeryx^ from the upper Eocene, is one of 

 the eai-liest selenodonts, but the most pronounced selenodont of the 

 Eocene is Oromeryx, perhaps a ruminant ancestor of the Deers. 



