1036 



CLASS AMPHIBIA. 



young, as we infer from Mastodonsaurus, in which alone this feature 

 has been observed, they were rhachitomous, as in the adult condi- 

 tion of the Archegosauridcz. The palatal vacuities were large and 

 approximated, as is well shown in fig. 966. This family may be 

 divided into two groups, according to the presence or absence of 

 an inner articular buttress at the proximal extremity of the mandible. 

 The group in which this buttress is present is represented by the 

 type genus Mastodonsaurus, best known by the huge Mastodonsaurus 

 giganteus (figs. 966, 967) of the Trias of Europe, which probably 

 attained a length of seven or eight feet, and ranged from the Mus- 

 chelkalk to the Rhsetic. Besides other European Triassic species, 

 this genus is also represented in the Lower Mesozoic (Maleri stage) 

 of India by a form closely allied to M. giganteus, and by another in 

 the Hawkesbury beds of New South Wales. Figure 968 shows the 



Fig. 968. — Transverse section of a segment of a tooth 

 of Mastodonsaurus giganteus. Greatly enlarged. (After 

 Oven.) 



Fig. 969. — Fragment 

 of jaw of one of the 

 Mastodonsaurida ; from 

 the Upper Gondwanas 

 of India, a shows the 

 section of a tooth. 



structure of a transverse section of a segment of a tooth of this 

 genus ; the mode of attachment of the teeth to the jaw being ex- 

 hibited in fig. 969. In the transverse section it will be observed 

 that there is one set of sinuous linear interspaces communicating 

 with the exterior, and a corresponding series (separated from each 

 other by the dental wall) of sinuous processes from the central pulp- 

 cavity. Other genera of this group are Capitosaurus (including 

 Cyclotosaurus), from the Keuper of Germany ; Trematosaurus, from 

 the Bunter of the same country, distinguished by its more slender 



