NATURAL SCIENCES OF PHILADELPHIA. 261 



by Dr. H. C. Yarrow, from near the town of Santa Clara, on the 

 west side of the Rio Grande. The specimen in its present con- 

 dition includes the condyle, angle, and ramus as far as the last 

 premolar, and supports the three true molars. The latter are 

 worn, indicating the full age of the animal. They still retain the 

 enamel surface of the sinus between the posterior and median 

 transverse crests, and the lower end of the sharp inner margin of 

 the anterior transverse crest. 



While the ramus exhibits the compressed form seen in A. mega- 

 lodus and A. meridianus, it differs from these and the A. crassus 

 in many striking respects. Thus the inferior margin near the 

 angle does not exhibit the protuberance and following contradic- 

 tion of the inner side seen in the first two species. In another 

 feature it differs from all the other species, i. e., in the form of the 

 ascending ramus. This rises very gradually from the basis of 

 the last molar, leaving a subhorizontal edentulous space behind 

 the latter as long as the second true molar. Its anterior face, 

 instead of being flat and bounded by strong, lateral, angular 

 ridges, as is the case in A. crassus and the two other species, is 

 rather narrowly convex. Instead of the usual ridge of the outer 

 side, the anterior border of the area of insertion of the masseter 

 muscle is marked by a permanent curved protuberant margin, 

 which is wanting in the three other species, the surface in them 

 being plane. Behind the condyle is seen the tuberosity character- 

 istic of the Rhinoceridae. The internal pterygoid fossa is well 

 marked. Rugosities for insertion on the lower border of the 

 angle are strong. 



The relations of the dentition of this species are also peculiar. 

 The last molar is nearly half as large again as that of specimens 

 of A. megalodus, and A. meridianus of similar dimensions of 

 ramus, and the teeth diminish in length anteriorly more rapidly 

 than in width. Thus, while the first true molar is as long as in 

 the two species named, the width is between one-half and one- 

 third greater. There are no external basal cingula. 



Measurements. M. 



Length of ramus from fourth premolar (behind) to mid- 

 dle of masseteric fossa 240 



Length of series of true molars 148 



" " first true molar 044 



Width " " " " 033 



Length " third " " 058 



Width " " " " 035 



Diameter of ramus at first molar 080 



Depth of ramus of third " 092 



The Phylogeny of the Camels Prof. Cope made the following 

 remarks on the extinct genera of camels : 



The line of descent of the horses has been already largely traced 

 by several paleontologists ; another series may now be regarded as 



