58 SCOTT. [Vol. V. 



The whole face has become shorter and deeper, and the anterior 

 nares are much higher and more oblique, while the posterior 

 nares have increased in height and are placed behind the molar 

 series. In P. occidentalis there is a small prelachrymal vacuity, 

 and the shape of the cranium is much like that of the llama, 

 with extended frontal zone, much shortened sagittal crest, and 

 very low occiput and inconspicuous lambdoid crest. There is a 

 small prelachrymal vacuity. On the other hand, the orbit, though 

 situated far back, is in relative size more like that of the camel, 

 and the posterior nares are almost precisely like those of that 

 genus. In P. angustidens, for an opportunity to study which I 

 am indebted to the kindness of Professor Cope, there is no pre- 

 lachrymal vacuity, the sagittal crest is much higher and longer, 

 and the lambdoid crest is much more prominent. In this cranium 

 the highest point is at the junction of the two crests : in P. occi- 

 dentalis it is in the middle of the parietal zone. The cranium of 

 P. angustidens thus strongly recalls that of the camel, as that 

 of the other species does the llama. In both the orbits are 

 enclosed by bone, and the palatal notches are deeper than in 

 the White River genus, while the nasals remain much longer 

 and narrower than in either of the recent genera. 



The mandible is known only in the case of P. occidentalism 

 and this is most like that of the llama ; but the ascending ramus 

 is relatively lower and wider, and the masseteric fossa is much 

 better developed. As compared with the mandible of Poebrothe- 

 riutn, the most important changes, aside from the general increase 

 in size, are the greater depth and robustness of the horizontal 

 ramus, the reduction of the angular process in length, and its 

 increase in height, and the less clear definition of the masseteric 

 fossa. 



The differences between the skull structure of Procamelus 

 and that of the modern genera are sufficiently indicated in 

 Rutimeyer's description already quoted. Unfortunately we know 

 too little about the skulls of the Pliocene and Quaternary forms 

 to enable us to trace these changes step by step. It should be 

 emphasized, however, that the skull of Procamelus unites pecu- 

 liarities both of Camelus and Auchenia, and that these characters 

 are not merely primitive features which have been retained by 

 one or other of the modern genera, but actual specializations ; e.g. 

 the position of the orbit and construction of the cranium on the 



