DINOTHERIUM. 609 



Tliosaurus ; the outer surface being nearly flat, and the rest of 

 the crown so convex as to describe a semi-circle : a ridge of 

 enamel along each border of the flattened side separates it from 

 the convex side of the crown. This fossil tooth presents a pecu- 

 liarity which I have not before observed, or found described, in 

 having the crown defended by two layers of enamel : the outer 

 and thicker layer has a minutely wrinkled surface and terminates 

 near the base of the crown by a finely plicated border, extending 

 lower upon the posterior and outer than upon the anterior and inner 

 sides of the crown : the thin and smooth layer of the enamel 

 extends to and defines the base of the crown, the outer layer 

 being co-extensive with the inner one only at the two boundary 

 ridges, and the inner layer being extended further upon the tooth 

 at its anterior and inner sides. The length of this tooth must 

 have been three inches when entire ; the circumference of the base 

 of the crown is two inches, nine lines. (1) 



224. Dinotheriiim. — The most extraordinary of extinct Pachy- 

 derms is that which Cuvier regarded as a gigantic Tapir, on 

 account of the character of the molar teeth, and which subsequent 

 discovery of the cranium and the enormous tusks of the lower jaw 

 (PI. 99, fig. 6) has proved to be a genus connecting the Tapiroid 

 with the proboscidian famiUes of Pachyderms. 



The permanent dentition of the genus Dinotherium is : — 



Incisors ^ ; canines ^ ; premolars — ^ ; molars — : = 22. 



2—2 ' 3—3 



the deciduous dentition was most probably : — 



-r . 1—1 . 0-0 , 3—3 „ 



Incisors — ; canmes — -; molars — - : = lb. 



1—1 U — o-~~o 



The first deciduous molar of the upper jaw has not yet been 

 detected ; it is highly probable that such a tooth existed, and I 

 concur with Professor Kaup in regarding the two deciduous 

 molars in situ, on each side of the fragment of the upper jaw of 

 the young Dinotherium which he has figured in Tab. 1, of his 

 * Ossemens Fossiles de Darmstadt', as the second and third. 



The crown of the second milk-molar supports two transverse 



(1) History of British Fossil Mammalia, PI. 306, fig. 105. 



R R 



