﻿THE DUCK-BILLS. 233 



anterior cornules are long and narrow, each forming a single 

 longitudinal ridge ; while each of the hinder pair consists of a 

 broad horny and cuspidate plate, subdivided by transverse 

 ridges into three cavities of different sizes. These cornules 

 are developed from the mucous membrane of the mouth under 

 and around the teeth, and they have beneath them hollows in 

 the bones which are the remnants of the sockets of the latter. 

 The teeth, whose function is subsequently performed by these 

 horny plates, are broad and shallow, and after being gradually 

 worn away by the sand swallowed with the food and the pro- 

 cess of masticaticn, are finally shed ere the animal attains its 

 full maturity. Whether these teeth correspond to the milk — 

 or the permanent dentition of higher Mammals, has not yet 

 been ascertained ; but it is not improbable that they may re- 

 present the former. The teeth themselves are broad, flat, and 

 low-crowned ; the upper ones (with the exception of the 

 minute anterior pair) having two tall cusps on the inner side^ 

 from which small ridges run downwards and outwards to the 

 outer side; while the latter has a peculiarly crenulated edge. As 

 already stated, these teeth are unlike those of any other existing 

 Mammal, although they present a very distant approximation 

 to those of the Banded Ant-eater. Their somewhat less remote 

 resemblance to those of the extinct Multituberculate Mammals 

 has been already mentioned. 



Distribution. — Queensland to the south of latitude iS°, New 

 South Wales, Victoria, South Australia, and Tasmania. 



History and Habits. — The Duck-bill was originally described 

 under the name of Platypus a?tatinus, which was Anglicised 

 into Duck-billed Platypus, but since the generic name had 

 been previously employed for another group of animals, it had, 

 by the rules of zoological nomenclature, to give place to the 

 later Ornilhorhynchus, although Shaw's specific name of 

 anathius still holds good. On these grounds it is likewise 



