PETERSON: THE AMERICAN DICERATHERES. 451 



Buried deep in the small round alveolus, the point of the upper permanent 

 incisor is found. Judging from the size of the alveole, the deciduous tooth was 

 rather small and had a root of more rounded outline than the permanent one, 

 and the crown was perhaps also of an entirely different shape. There is no canine 

 present and, if there were a deciduous canine in this individual, it dropped out 

 early and the alveole was closed, there being in this region a small groove which 

 extends for a short distance back of the maxillary-premaxillary suture. If there 

 was a deciduous first premolar in the Diceratheres, it was possibly shed very early 

 in life.^" P^ is somewhat worn, but not enough to lose the characters of the grinding 

 face. (See PI. LXV, Fig. 2.) The ectoloph is, as usual, well developed, the 

 protoloph is less prominent than the metaloph, which gives to the tooth the char- 

 acteristic triangular outline. The post-fossette is sometimes constricted in such a 

 manner as to form an isolated fossette on the metaloph on further wear, while the 

 main post-fossette continues to the posterior edge of the tooth. This fossette is 

 not always present. D.P- is considerably worn, but the detailed structure is yet 

 easily made out. The tooth is longer than the permanent tooth, the ectoloph is 

 heavy, the protoloph is well developed internally as is also the metaloph. The 

 crista is enormously developed, extending on an even internal line with the proto- 

 and metalophs. In a young or unworn tooth this ridge is often constricted so 

 as to form an internal tubercle, which on further wear unites with the true crista. 

 In the young of the John Day forms both the crista and this internal tubercle are 

 less developed and apparently entirely separated, judging from the material in 

 the American Museum. This is admirably illustrated on PL LXV Fig. 3. The 

 crochet of D.P- in D. cooki is quite distinct though much less developed than the 

 crista, and the cingulum is well developed on the internal face of the tooth. In 

 excavating the maxillary above D.P- it is seen that P- is quite well advanced. See 

 PL LXV, Fig. 1. D.P^ is well worn. The median valley is open, but the crochet is 

 evidently united with the ectoloph, while the post-fosette is isolated by wear of 

 the tooth. There is a small tubercle on the internal cingulum in the median 

 valley. D.P^ has the well developed crochet still separated from the ectoloph, 

 but the crista is rather poorly developed or wanting. The median valley is open 

 and, as in the preceding tooth, there is a small tubercle on the cingulum at the 

 exit of the valley. The post-fossette is broad and open. M' is fully erupted and 

 has already received some wear. The ectoloph is yet quite thin, but in excavating 



™ If P' in Diceratherium did not succeed a milk-tooth in extremely early stages of the animal, this 

 tooth may be regarded as a persistent milk-tooth which would agree with the studies of Huxley ("Anatomy 

 of Vertebrate Animals," p. 362); Lydekker ("Notes on the Dentition of Rhinoceroses," Jour. Asiatic 

 Society of Bengal, Vol. 49, 1880, pp. 1.35-6). 



