1334 CLASS MAMMALIA. 



Phosphorites, the dentition is almost, if not quite, indistinguishable 

 from that of Leptomeryx, but cannon-bones are found in both limbs, 

 although the union of the factors in the anterior ones is less complete 

 than in the others. These two genera apparently connect Gelocus so 

 completely with the cervine Palcsomeryx, that we can have no hesi- 

 tation in regarding them as representing the direct line of the 

 descent of the Cervidce from the Dichodontidce ; while we must con- 

 sider the existing Tragulidce as lateral offshoots from some nearly 

 allied primitive stock. Hyper tragulus, from the Miocene of North 

 America, appears to be a form closely allied to Leptomeryx, but with 

 the metatarsals separate. 



Family Poebrotheriid^e. — We must here leave for a short time 

 the connection between the Tragulidce and the Cervidce, to consider 

 the Camels and their allies, whose nearest existing relations are to 

 be found in the former family. The Poebrotheriidce are represented 

 typically by the genus Poebrotherium, of the North American Mio- 

 cene, in which the dental formula is I. ~, C. -, Pm.-, M. -. The 



3 ! 4 3 



structure of the cheek-teeth is selenodont ; in the feet the third and 

 fourth metacarpals remain distinct, the second and third being rudi- 

 mentary ; the carpus has a trapezium ; and the navicular and cuboid 

 are not fused together. The structure of the cervical vertebrae is 

 the same as in the Camelidce, of which this family may be regarded 

 as the ancestral type ; but in other respects there are signs of 

 affinity with the Tragulidce. The type species of Poebrotherium was 

 scarcely larger than a Fox. In the John Day Miocene of Oregon 

 an allied form has received the name of Gomphotherium ; while 

 Leptotragulus of the Upper Eocene of the United States may be 

 the ancestral form of both the Miocene genera. 



Family Camelice. — In the Camels the cheek-teeth are seleno- 

 dont and quadricolumnar, but of somewhat simpler structure than 

 those of the following families. The navicular and cuboid remain 

 distinct, but the metapodials unite to form a cannon-bone. At 

 least one pair of upper incisors is present; and in the cervical verte- 

 brae the arterial canal passes obliquely through the anterior part of 

 the pedicle of the neural arch, and is thus confluent posteriorly with 

 the neural canal ; a similar condition prevailing in Macrauchenia 

 among the Perissodactyla. At the present day this family is repre- 

 sented by Camelus of the Old, and Auchenia of the New World ; 

 but it appears to have originated in the latter, where a large number 

 of forms have been found. The most generalised member is 

 Protolabis, of the Miocene of the United States, in which the denti- 

 tion is numerically the same as in Poebrotherium, on which grounds 

 Professor Cope makes it the type of a distinct family. In Pro- 

 camelus (fig. 1210, b, c) of the Lower Pliocene or Upper Miocene 



