1887.] 



393 



[Cope. 



the Cainelidne, the consolidation of the bones of the feet and a great 

 reduction in the numbers of the incisor and pi'emolar teeth. The embry- 

 onic history of these parts is as follows : In the fcetal state all the Ru- 

 miuantia (to which the camels belong) have the cannon bones divided as 

 in Poebrotherium ; they exhibit also incisor teeth, as in that genus and 

 Protolabis. Very young recent camels have the additional premolar of 

 Pliauchenia. They shed this tooth at an early period, but very rarely a 

 camel is found in which the tooth persists. The anterior premolar of the 

 normal Camelus is in like manner found in the young llama (Auchenia), 

 but is shed long before the animal attains maturity. I may add that in 

 some species of Procamelus caducous scales of enamel and dentine in 

 shallow cavities represent the incisor dentition of Protolabis. 



In greater detail, the extinct American forms of this line are distributed 

 as follows : 



The total number of genera, nine ; of species, twenty-six. 



The development of the brain displays the same progress that has been 

 shown by Lartet and Marsh to have taken place in other lines of Mam- 

 malia. The figures which I have given of the brain, show that while Proca- 

 melus occidentalis is inferior to the camel in the size and development of 

 the convolutions of the hemispheres, it is in advance of the Poebrotherium 

 vilsoni in these respects. 



The development of the camels in North America presents a remark- 

 able parallel to that of the horses. The ancestors of both lines appear 

 together in the Wasatch or lowest Eocene, and the successive forms de- 

 velop side by side in all the succeeding formations. Camels and horses 

 are standard types in all our Tertiary formations ; and they must be 

 learned by any one who wishes to distinguish readily the horizons one 

 from the other. The horse-forms are more numerous in all the beds, in 

 individuals as well as in species. Both lines died out in North America, 

 and of the two, the camels only have certainly held their own in South 

 America. The history of the succession of horses in Europe, although 

 not as complete as that in America, extends over as wide a period of time. 



PROC. AMER. PHILOS. SOC. XXIV. 126. 2x. PRINTED DEC. 3, 1887. 



