170 MK. E. T. NEWTON ON A SKULL OF TKOGONTHERIUM CUVIERI 



3. Dental Characters of the Trogontherium of the Forest Bed. 



In order rightly to compare the dentition of the skull ahove described, it is necessary 

 to bear in mind the changes which the patterns of the teeth undergo during wear, as 

 shown by a study of the many teeth which have been obtained from the Forest Bed. It 

 will be desirable, therefore, to give a brief account of the entire dentition as at present 

 known. 



The incisors of both upper and lower jaws are larger than in the Beaver, the 

 enamelled fronts are much more convex, and the enamel itself is rough and not smooth. 

 The upper incisors are nearly circular in transverse section, and seem to have been 

 thicker than the lower ones, although the entire tooth forms a segment of a smaller 

 circle. The lower incisors are elliptical in transverse section, and, in some cases at 

 least, are worn to a point (or nearly so) and not to a chisel edge like the flat-fronted 

 incisors of the Beaver. 



The cheeli-teeth are all characterized by liaving the enamel folds connected with the 

 exterior of the tooth for only a short distance from the summit, and consequently at an 

 early stage of wear the folds become isolated. 



JJpper 'pm. 4. — This is the largest of the upper cheek-teeth; it has one inner and 

 tliree outer folds, and all the examples of tlris tooth I have yet seen retain these four 

 areas of enamel. 



Upper m. 1 and m. 2. — These teeth have each one inner and three outer folds (m. 2, 

 fig. 5) ; but the posterior outer fold is soon isolated and then worn out, reducing the 

 folds to three, as in m. 1 (fig. 5) of the skull above described; and then the anterior 

 outer enamel area is lost, leaving only two folds, as in the maxilla described by 

 Sir R. Owen {loc. cit.) (m. 1 & 2, fig. 6). 



Upper in. 3 has one inner and four outer folds, as shown in the skull above described 

 (m. 3, fig. 5) ; but the anterior outer fold is small and soon lost, as exemplified in the 

 maxilla described by Sir R. Owen (m. 3, fig. 6). This tooth is longer from before 

 backwards than either of the other two molars, but its width is about the same. 



Loiver pm. 4. — This is the largest of the lower cheek-teeth; it has one outer and 

 three inner enamel folds ; sometimes there is an additional, very small enamel area at 

 the front of the tooth. 



Lower m. I is the smallest of the lower true molars ; it has one outer and three inner 

 folds, but these may be reduced by wear to two, as in some of the upper molars. 



Lower m. 2 is a little larger than m. 1, but not so large as m. 3 ; it has four folds, 

 the same as in m. 1, and probably by wear they may be reduced to two. 



Lower m. 3. — This tooth is perhaps a little larger than m. 2, but not nearly so large 

 as pm. 4. There are four folds as in the other true molars, and these doubtless become 

 reduced in number by wear, but definite evidence on this point is wanting. In one 

 example some of tlie folds of molars 2 and 8 have become broken up into small islands. 



A milk-tooth preceding the lower pm. 4 has been found in two or three instances. 



