58 



the top, unlike the wearing- exhibited in any modern form 

 that has come under our notice. The others have their 

 crowns broken, but indicate a nearly subequal series, with the 

 last slightly the largest. 



The canines have long, recurved compressed fangs, with 

 rather short crowns, which are circular in section. They 

 are much larger than in Procamelus or Protolabis of Pliocene, 

 or the modern camels. (S^e X., Figs. 3, 5, 6, 7.) 



The first premolar is the onl}'^ one of the molar series pre- 

 served ; its crown is chipped considerably, but nevertheless 

 shows that it had one fang and no basal ridge. It resembles 

 the incisors in form, but is slightl}' narrower and longer. 



The genus ItJiygramuiodon has been placed for the present 

 under the genera incertes sedis ; but its chief features point to 

 an unmistakable affinity with the ruminants. It is probable 

 that Ithygranunodon was the representative and the ancestor, 

 in the eocene age, of that type of ungulates of which the 

 camel and llama are the modern forms. 



The hne of descent of the camels was -first indicated in 

 the Proceedings of the Philadelphia Academy, 1875, p. 262; 

 then in the Bulletin No. i, 1874, p. 25, of the U.S. Geologi- 

 cal Surveys of the Territories, (Government Report of Ex- 

 plorations of 1873, PP- 498-500); and lastly in U. S. Geogra- 

 phical Surveys of Territories, vol. iv., pp. 341-44. 



In the above writings, Professor Cope traces the develop- 

 ment of the modern camels from the miocene genus Poebro- 

 therium, Leidy, showing the modifications found in Proca- 

 melus, Leidy, and Protolabis, Cope, of the succeeding age. 



From the last work (Wheeler's Survey, vol. iv., p. 342), 

 we will quote at length : 



" The evolution of the existing types of Camelid^e is a good 

 illustration of the operation of the laws of acceleration and 

 retardation. In evidence of this we may follow the growth 

 of the foot and dentition of the most specialized, and there- 

 fore the terminal genus of the series, the American Aiichenia 



. It is well known since the time of Goodsir, that the 



embryos of ruminants exhibit a series of superior incisor 

 teeth which disappear early. It is probable, but not certain, 

 that in the miocene genus Poebrotherium, as in various 



