MAMMALIA. 



85 



may perhaps belong to a similar animal. In the Triassic Table-ease 

 period, however, the Theriodont Eeptiles so closely approached 14a " 





ill 



>- f 'I, 



....... L^P-": J^Wmmmt. 



*■ 



mm 



I) 



Pig. 81. — Skull of Tritylodon longievus, palatal view (a) and upper view (b), 

 incomplete behind, from the Karoo Formation (Trias) of Basuto- 

 land, South Africa ; two-thirds nat. size. (Gallery of Fossil Reptiles, 

 Table-case 32.) 



the lowest mammals that skeletons alone hardly suffice for 

 the exact determination of their affinities. 



Tritylodon and Theriodesmus are now arranged with the 

 Theriodonts in the Gallery of Fossil Eeptiles (Table-case 32). 



Order XII.— MONOTREMATA. 



The existing monotremes of the Australian region are 

 evidently the much - altered 

 survivors of a very ancient 

 race, and owe their escape from 

 extinction to their small size 

 and burrowing habits. Their 

 predecessors, however, are 

 almost unknown. Plaster 

 casts of some limb-bones of a 

 large Echidna from the Wel- 

 lington Caves, New South 

 Wales, are exhibited in Table- 

 case 14a. 



Table-ease 

 14a. 



Fig. 82. — Eight lower molar teeth 

 of the existing Australian 

 Monotreme (Ormthorhynchus) , 

 showing their multituberou- 

 late crown ; three times nat. 

 size. (After C. Stewart.) 



