1898.] JVortman, Extinct Ca/nelidce of North America. 139 



is always found first in the old individuals ; its further advance 

 has consisted in reducing the time of its appearance to such an 

 extent that it is now altogether intra uterine. I leave for a future 

 paper the discussion of these important facts in their relation to the 

 question of the transmission of acquired characters. I may state 

 here, however, that they furnish very strong presumptive, if not 

 conclusive, evidence of the transmission of a pathological change. 



The modifications of the skull include some minor changes in 

 the position of the orbit, its inclosure by a complete bony rim, a 

 broadening of the frontal region and a shortening of the nasal 

 bones. There have also occurred some modifications of the 

 tympanic bullae and a change in the position of the posterior 

 nares. The most important of all the modifications connected 

 with the skull, however, are found in the dentition, and here the 

 changes are quite as profound as have occurred in any other 

 group of mammals within the same length of time. In Protylopiis 

 the structure of the molars is, to a large extent, intermediate 

 between the bunodont and selenodont pattern. This is especially 

 seen in the lower molars, the internal cusps of which are rather 

 more conical than crescentic ; the outer cusps are not perfectly 

 crescentic, and the crowns of all the molars are very short. The 

 lower canines are small and incisiform, the inferior incisors are 

 sub-erect, and there is evidence of the fact that these teeth had a 

 more or less effective bite against the upper ones. 



In Poebrotheriion the crowns of the molars are much more 

 elongated and the crescents fully developed. The lower canine 

 is yet incisiform in the older species, P. wilsoni, but has begun to 

 assume the caniniform shape in the later P. labiatuin. The lower 

 incisors have a very procumbent position, but while yet opposing 

 the superior incisors, the effectiveness of the bite is considerably 

 diminished on this account. The only important change in the 

 teeth of the John Day species is seen in the reduction in size of 

 the first upper premolar and the assumption of the caniniform 

 shape of the lower canine. The inferior dentition of Protolabis is 

 not known, but an important change has taken place in the second 

 superior premolar, in that it is much reduced in size. 



If the specimen which I have referred to Procamelus robustus 

 is normal, it offers the first evidence of the diminution in size, 



