OF SOUTH CAROLINA. 23 
of trituration. In the Mammoth the plates are disposed in series parallel with the shorter or trans- 
verse diameter of the tooth, and connected at the extremities. "The molars of the Mastodon, on the 
contrary, have prominences on the crown, covered by a thick coat of enamel, which appears more 
or less removed by detrition in adult individuals. The tusks of these animals often occur in the 
fossil state, and may always be detected by the peculiar “twilled” appearance of the ivory, which, 
when once observed, cannot be mistaken for any other substance. In Carnivora the teeth are 
covered with enamel, but no piates extend through the body of the teeth. 
No animals but those of the class Mammalia have teeth with more than one fang or root. The 
roots of the teeth of sharks are divided into two lobes, yet can scarcely be mistaken for the teeth of 
animals of this class. ‘The articular surfaces of the vertebree are always flat or slightly concave. 
The cervical vertebre of the horse present an apparent exception; but a single comparison with 
the true ball and socket joint of reptilia will prevent mistakes on this point. 'The processes are 
imited to the centrum by anchylosis, or, as Professor Owen expresses it, are exogenous, and distin- 
guish mammalian vertebra from those of reptilia in those fossils where the ball and socket joint 
of the latter is absent, as in Ichthyosaurus. 'The number of vertebre in the spinal column is various, 
hut constant in certain portions of it. There are, with one or two exceptions, seven cervical 
vertebre ; the average number of dorsal vertebrae is twelve. ‘The caudal vertebre are quite 
variable, and sometimes numerous. 
The bones of the limbs in Mammalia are in general firm and elastic ; the interior filled with 
tissue, having a cancellated structure, or presenting a medullary cavity. In the bones of cetacea 
which have no medullary cavity, the cancellated structure is coarse and conspicuous. Certain 
bones of the ear of cetacea, which are nearly as hard as flint, are found in our tertiary formation. 
They are oblong and irregular, with depression on one side: they have been called ofolithes. 
The following list comprehends nearly all the genera that are found fossil of this class. 
1. Order, Quadrumana. 5. Order, Rodentia. 
Macacus— Monkey. Castor— Beaver. 
2. Order, Cheirotherium. Casteroides. 
Rhinolophus— Bat. Mus—Rat. 
3. Order, Carnivora. Lepus—Hare. 
Talpa— Mole. 6. Order, Edentata. 
Sorex— Shrew-mouse. Megalonyx. 
Amphitherium. Megatherium. 
Ursus— Bear. Mylodon. 
Meles— Badger. Scelidotherium. 
Putorius— Pole cat. Macrauchenia. 
Canis— Wolf. Toxodon. 
Hyena. 7. Order, Pachydermata. 
Felis—Cat. Elephas. 
Phoca—WNeal. Mastodon. 
4, Order, Marsupiata. Rhinoceros. 
Didelphis— Opossum. Hippopotamus. 
Phascolotherium. Lophiodon. 
Tapi. 
