MAMMALIA. 



85 



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

 period, however, the Theriodont Eeptiles so closely approached ■'■^*- 



Fk;. 81. — Skull of Tritj/lodoii Iong(revus, palatal view (a) and upper view (6), 

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

 land, South Africa ; two-thirds uat. 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 Therriodcsmus are now arranged with the 

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



Order XII.— MONOTREMATA. 



The existing monotremes 

 evidently the much-altered 

 survivors of a very ancient 

 race, and owe their escape from 

 extinction to their small size 

 and l)urrowing habits. Their 

 predecessors, however, are 

 almost unknown. Plaster 

 casts of some limb-bones of a 

 large Echidna from the Wel- 

 lington Caves, New Soutli 

 Wales, are exhibited in Table- 

 case 14a. 



ire 



Table-case 

 14a. 



Fig. 82. — Right lower molar teeth 

 of the existing Australian 

 Monotreme(Or)iif/(oW(.i7»c/i»s), 

 showing their nmltitubercu- 

 latc crown ; three times uat. 

 size. (After C. Stewart.) 



