220 HISTORICAL PALAAONTOLOGY. 
Placodus, again, the teeth are in distinct sockets, but resemble 
those of many fishes in being rounded and obtuse (fig. 153), 
forming broad crushing plates 
adapted for the comminu- 
tion of shell-fish. There is a 
row of these teeth all round 
the upper jaw proper, and a 
double series on the palate, 
but the lower jaw has only a 
single row of teeth. Placodus 
is found in the Muschelkalk, 
and the characters of its den- 
tal apparatus indicate that 
k it was much more peaceful 
ja S Baa unde paurace of the wer in its habits than its asso- 
chelkalk, Germany. ciates the Nothosaur and Si- 
mosaur. 
The Triassic rocks of South Africa and India have yielded 
the remains of some extraordinary Reptiles, which have been 
placed by Professor Owen in a separate order under the name 
of Anomodontia. ‘The two principal genera of this group are 
Dicynodon and Oudenodon, both of which appear to have been 
large Reptiles, with well-developed limbs, organised for pro- 
gression upon the dry land In Oudenodon (fig. 154, B) the 
jaws seem to have been wholly destitute of teeth, and must 
have been encased in a horny sheath, similar to that with 
which we are familiar in the beak of a Turtle. In Daecynodon 
(fig. 154, A), on the other hand, the front of the upper jaw 
and the whole of the lower jaw were destitute of teeth, and 
the front of the mouth must have constituted a kind of beak; 
but the upper jaw possessed on each side a single huge conical 
tusk, which is directed downwards, and must have continued 
to grow during the life of the animal. 
It may be mentioned that the above-mentioned Tniassic 
sandstones of South Africa have recently yielded to the re- 
searches of Professor Owen a new and unexpected type of 
Reptile, which exhibits some of the structural peculiarities 
which we have been accustomed to regard as characteristic 
of the Carnivorous quadrupeds. The Reptile in question has 
been named Cyzodraco, and it is looked upon by its distin- 
guished discoverer as the type of a new order, to which he has 
given the name of Zheriodontia. The teeth of this singular 
form agree with those of the Carnivorous quadrupeds in con- 
sisting of three distinct groups—namely, front teeth or zucisors, 
eye teeth or canines, and back teeth or molars. ‘The canines 
