THE PLESIOSAURS. 513 
Another form was still more like the turtles, the jaws being 
toothless and enclosed in a nipping, horny beak. In Lys- 
trosaurus (Fig. 450) the head was blunt, the jaws armed in 
front with stout teeth, and behind with canine teeth ; and 
these animals, anticipating in their dentition the lions and 
tigers, were called by Owen Theriodonts (beast-toothed). 
These forms lived during the Permian and Triassic times.* 
Order 8. Sauropterygia.—The Plesiosaurus is the type 
q 
< 
S88 
ti 
iil 
i = Prf 
Som <a ‘ H ZZ dt NV 
Pro = i Soft 
ie & . 
Se the Zot 
— pee Prax 
| } 
seston ~~ Mae 
An— qe» | Y 
D ——----. 
| 
a 
: a 
Fig. 450.—Skull of Lystrosaurus frontosus from CapeColony. | Profile. Lettering 
as in Fig. 443 and 444, with the following additions: Ztvom, ethmovomerine ; Sph, 
sphenoid ; pro, Prootic; Ptler, Pterygoid ; Col, Columella; Hetp, Ectopterygoid ; 
ubart, subarticular bone.—From Cope. 
x 
&, 
Subar. 
of this extinct order. The Plesiosaurs were somewhat like 
the Ichthyosaurs, swimming by paddle-like feet, but the neck 
was very long, and the head rather small. The largest true 
Plesiosaur was about nine metres in length. They abounded 
during the Jurassic and Cretaceous period. During the lat- 
ter period off the coast of New Jersey and in the seas of 
Kansas flourished huge Plesiosaurian reptiles, such as Hlas- 
mosaurus, Which had an enormous compressed tail. The 
* The Theromorphs were the earliest, most generalized reptiles. 
