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 mastication, 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 18°, New 
| South Wales, Victoria, South Australia, and Tasmania. 
| History and Habits—The Duck-bill was originally described 
‘under the name of Platypus anatinus, 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 Ornithorhynchus, although Shaw’s specific name of 
_anadinus still holds good. On these grounds it is likewise 
