OF SOUTH CAROLINA. 35 - 
have the aperture notched or extended into a canal. Some exceptions there are to this character- 
istic, but they are not numerous. And the facts stated furnish the Geologist with the means of 
discriminating between marine and freshwater deposits. 'The marine Gasteropods generally inhabit 
shallow water, and hence their abundance in a deposit would indicate a littoral formation. 
They diminish greatly in number as we proceed downwards in the geological series, and below 
the cretaceous formation they become comparatively rare. Some genera, however, date as far back 
as the Silurian rocks. . 
Pleurotomaria and Kuomphalus are remarkable genera that oceur in the oldest fossilliferous 
rocks. ‘The shells of this class abound in the Tertiary formation of the United States. 
Class Pteropoda.—A single fossil shell of this class is found in the post-pliocene of South 
Carolina. It belongs to the genus Hyalea. 
» Class Lamellibranchiata—-The oyster and clam are examples. They have bivalve shells, and 
the opening and shutting of the shells is effected by the joint action of a ligament, placed at the 
hinge, and muscles attached to the shells. The class is divided into two orders: those with one 
muscle, called Monomyaria. and those with two, called Dimyaria. T'o the first belong the oyster, 
gryphza, anomia, plagiostoma, plicatula, hippurites, &c. The latter is a very remarkable fossil, 
whose affinities are but little known. It is a conical or cylindrical shell, having on the inside two 
longitudinal ridges. At the base there are sometimes cells, formed by transverse septa. The upper 
valve is placed like a cover on the aperture of the conical valve. 
In the cretaceous formation of Alabama these shells are found of considerable size, amounting 
sometimes to one foot in diameter. Fragments of the shell may be known by its cancellated and 
cellular structure. 
Class Brachiopoda—The molluscs of this class are furnished with ciliated arms, spirally coiled, 
and supported by a spiral calcareous appendage, which is often found preserved in fossil Bra- 
chiopods. The shells are bivalve. They existed in vast numbers in the early geological periods. 
The oldest bivalve shells are of this class; some of which are confined altogether to the lowest 
fossilliferous rocks, whilst a few are living in the seas of the present period. Among the latter are 
Lingula and 'Terebratula. In the New York system the Lingula is the first bivalve that makes its 
appearance. ‘The genera of this class that are found most abundant in the Silurian rocks are 
Delthyris, Atrypa, Orthis, Lepteena, and Pentamerus. ‘ 
Sup-K1nepom RapiatTa. 
The animals of this sub-kingdom are distinguished, as the name implies, by having their parts 
so arranged as to radiate from a centre. The common star-fish is a good example. They are soft 
and naked, or covered with calcareous plates symmetrically arranged. 
Those who visit the coast of this State have ample opportunities of studying the interesting 
living forms of this sub-kingdom. The soft and lower forms may be seen floating, at certain 
seasons, in the water. ‘The star-fish is left in numbers by every tide, and the scutella is found 
slightly covered in the sand. The echinus and rarer spatangus are torn from their sandy beds 
and thrown on the strand by every storm. It is only, however, with those furnished with hard 
coverings that the Paleontologist is concerned, and these belong to the class Radiaria, and to the 
