TTNGULATA. 



alternate arrangement ; there are never fewer than three such ridges 

 in the last milk- and the first true molars ; and the intervening 

 valleys may be either entirely open, or blocked by accessory tubercles, 

 or completely filled with cement J . 



Family DINOTHERIID^]. 



All the teeth of the permanent series are in use at the same time, 

 the premolars succeeding the milk-molars in the normal manner. 

 In the one known genus none of the cheek-teeth have cement, or 

 carry more than three ridges : in the true molars these ridges are 

 continuous and the valleys open ; but in the upper premolars the 

 former are more or less interrupted, and are connected by a longi- 

 tudinal external ridge, a similar submedian ridge occurring in the 

 lower premolars. This lophodont structure of the premolars is a 

 character connecting DinotJierium with the Perissodactyla, and is not 

 improbably evidence of their original community of descent. In 

 section the incisors do not present decussating striae. The upper 

 cheek-teeth of DinotJierium giganteum are figured in the accom- 

 panying woodcut. 



' Fig. 1. 



DinotJierium giganteum.— -The left upper cheek-dentition ; from the Middle 

 Miocene of Samaran (Gers), France. £. p, premolars ; a, true molars. 

 (After Gaudry's ' Enchainements.') 



1 For other characters see Marsh, ' Monograph of the Dinocerata,' pp. 174-5 

 (1884), and Flower, 'Encyclopaedia Britannioa,' 9th ed. toI. xv. pp. 423-5 

 (1883). 



