522 
MOLLUSCA. 
THE CAEDIACEA. 
These include a great variety of species — two liundred in number — bearing the general name 
of CocMe. Many of them are elegantly marked with radi- 
ating ribs, and these are sometimes ornamented with spines 
of various forms. They are usually active animals, often 
springing to a considerable height by means of the strong- 
bent feet. They generally live concealed in the mud. The 
Common Cockle, Cardium edule, is eaten in large quantities 
on the coasts of Europe, The C. Junonce is a very beautiful 
species. The great assemblage of the different kinds is in the 
Indian Ocean, though some of the species are found in all seas. 
Several small species, as the 0. Greenlandicum^ the C. Mar- 
tinii, &c.y are found on our coasts. 
THE CAEDIDM JUNONiE. 
TEE HIPPOPUS MACULATUS. 
THE CHAMACEA. 
This group includes several genera of bi- 
valved mollusca, sometimes called Clams, 
and mostly found in trojDical countries ; cer- 
tain species are the largest animals belong- 
ing to this division of the animal kingdom. 
Of the genus Ckama, there are more 
than twenty species, generally found at- 
tached to submarine substances as rocks 
and corals ; they are of various forms and 
sizes, though generally large. The Giant 
Clam, Tridacna gigas, is the largest of 
known shell-fish, the two valves some- 
times weighing five hundred pounds, and 
the animal from twenty to thirty pounds. 
It is found along the shores of the Polyne- 
sian and Asiatic Islands, where the flesh is 
eaten raw by the natives. The interior of 
the shell is beautiful, being white and like 
polished marble ; the form is also elegant, 
whence it is much sought for as an orna- 
ment for fountains, grottoes, and flower- 
gardens. It is also employed as fonts for 
holy water in Catholic churches in Europe. 
One of enormous dimensions is used for this 
purpose in the church of St. Sulpice, Paris. 
The shells of the Hippopus maculatus are 
smaller but are very beautiful, and are used 
in the manufacture of various ornamental 
articles, as inkstands, &c. 
Broderip says of the chamacea, that they 
have been found at various depths, from the 
surface to seventeen fathoms ; their shape is 
usually determined by the body to wdiich 
they are fixed; their color seems to be in- 
fluenced by their exposure to the light. The 
byssus by which the T. gigas is attached to 
the rocks is so firm and tough, that it can 
only be severed by an ax. 
