Cope.] ^ob [Oct. 7, 



But one genus of Elotheriid^ is known. The character of the feet, 

 reduced to but two metapodials in a bunodont genus of the Lower Mio- 

 cene or Oligocene, surprised Kowalevsky, wlio first determined the fact, 

 and has excited simihir feelings in otlier naturalists. But the precocious 

 diminution of the lateral digits has been already observed in various 

 primitive genera, as Pantolestes and Dichobune, and from one or perhaps 

 both of these forms Elotherium was derived. In its dental characters it 

 is of the simple suilline type. The type early ceased to exist, its latest 

 forms being American, and some of them rivaled the rhinoceroses in 

 dimensions. 



The Ltstriodontid^e and Merycopotamid^ include but one genus 

 each, though others probably will be discovered. I therefore turn to the 

 Oreodontid^ which embraces a larger number of forms. Its characters 

 are as follows : 



Dentition : superior incisors present ; molars selenodont. Cervicals 

 with the transverse processes perforated by the vertebrarterial canal. No 

 alisphenoid canal. Ulna and radius, and tibia and fibula distinct. Meta- 

 podial bones four on each foot, with incomplete distal trochlear keels. 

 Lunar bone not supported by magnum. Navicular and cuboid bones dis- 

 tinct. The details of the structure express various affinities. The axis is 

 intermediate between that of the suilline and ruminant Artiodactyla ; the 

 otlier cervicals are suilline, while the remaining vertebrae are ruminant. 

 The scapula is ruminant, not suilline ; while the humerus is like Anoplo- 

 therium. The radiocarpal articulation is intermediate between that of 

 hogs and ruminants. The unciform supports the lunar bone. The sacrum 

 is ruminant, the ilium suilline. The femur and tarsus are much like those 

 of the peccary. 



The known genera of this family are the following : 



A. Orbit complete ; premolars four, the fourth with one external 

 crescent. First premolar below functioning as canine. 

 a. No facial vacuities. 

 Premaxillaries distinct ; otic bullae not inflated ; five digits in manus 



Oreodon Leidy. 

 Premaxillaries distinct ; otic bullse inflated ; four digits in manus 



Eucrotaplais Leidy. 



Premaxillaries coossified ; otic bullae inflated Merycochosrvs Leidy. 



aa. Facial vacuities present. 

 Premaxillaries coossified, dentigerous ; vacuities prelachrymal only 



Merychyus Leidy. 

 Incisors six above, persistent ; vacuities prelachrymal and prefrontal ; 



nasal bones much reduced LeptaucJienia Leidy. 



Incisors very few, caducous ; vacuities very large Cyclopidius Cope. 



A A. Inferior premolars three. True inferior canine functional. 

 Inferior incisors one on each side Pitliecistes Cope. 



