No. i.] OSTEOLOGY OF PCEBROTHERIUM. 71 



the position of the orbits and the extension of the frontal zone, 

 with the camel in the shape and position of the posterior nares. 

 But this objection is of no great weight, for this differentiation 

 is as difficult to explain on the assumption that Procamclns is a 

 side branch. The two species P. occidentalis and P. angustidens 

 very strongly suggest themselves as the starting-points of the 

 llama and camel series respectively. 



Protolabis is obviously the connecting link between Procaine- 

 lus and Poebrotherium ; and so far as known, is exactly what it 

 should be to assume this position. 



Poebrotherium has frequently been regarded as ancestral to 

 the camels only, but its relation to the llamas is quite as un- 

 mistakable. Branco's suggestion (No. 4), which was adopted by 

 Schlosser (No. 27, p. 49), that Leptanchcnia is the earliest known 

 member of the Anchenia line, I have elsewhere shown to be 

 entirely untenable (No. 31, p. 356). 



Leptotragnlns is so very like Poebrotherium that no one can 

 hesitate to regard it as the forerunner of the White River genus. 

 Every known detail of its structure thoroughly confirms this 

 view. 



The position of the Bridger genus Homacodon is much less 

 clear, for as yet only the most meagre accounts of that form 

 have been published ; but so far as it is known, it gives us every 

 reason to believe that it is connected on the one hand with 

 Pantolcstes and on the other with Leptotragulus. 



If these conclusions are correct, it follows that the Tylopoda 

 are but remotely connected with the true ruminants, and that 

 they have no common ancestors nearer than the DicJiobunidce, 

 to which Schlosser also traces the Pecora. However this may 

 be, no one will dispute the view that Pcebrotherium cannot be 

 ancestral to any of the ordinary ruminants ; and, therefore, that 

 all the structural points in which the modern Camclida agree 

 with the Pecora, but which do not occur in Poebrotherium , 

 must have been independently acquired. As we have already 

 seen, Riitimeyer reached this same conclusion from the study of 

 the existing forms alone. 



I have elsewhere given my reasons (No. 31, p. 389) for believ- 

 ing that the oft-repeated view of the connection between the 

 Oreodontidce and the CamclidcB is altogether untenable, and I 

 need not repeat them here. The present investigation further 



