3fi6 Tkidacnid^. MOLLUSCA. Pholadina. 
salt water for a time, it has probably been carried across 
tooth in each valve, two posterior lateral teeth in one, 
seas attached to the bottoms of ships, and in this manner 
and a single one in the other. 
it appears to have reached England, and has become 
THE GIANT CLAM SHELL {Tridacna gigas) is very 
so common in our canals as to be much more abundant 
large, with great imbricated squamous ribs. Its size and 
than many of our indigenous mollusks. James de 
weight, combined with the beautiful marble-like appear- 
Carle Sowerby first described it as British. This was 
ance of its interior, have always caused it to be sought 
in 1824, and he stated that it was found in abundance 
after as an ornament for grotto work or for garden 
attached to shells and timber in the Commercial Docks, 
fountains; and, indeed, as Mr. Broderip remarks, the 
and that the animal was used as bait for perch. Mr. 
valve of a large individual forms a very picturesque 
Stark found it in the Union Canal, near Edinburgh, in 
basin for catching the clear falling water, and transmit- 
1834; and the Rev. J. Berkely observed it in the river 
ting it through the deep interstices of its indented edge 
Nen in 1836, though he believed it had been introduced 
to the reservoir below. In Roman Catholic countries. 
from Wisbeach, on timber, in 1828. Thus it would 
the valves of the huge shell are sometimes used as 
appear to have found its way into Britain at several 
“ benitiers,” or vessels for containing holy water. A 
points, and is now common in many parts of the country ; 
pair, so used, may be seen in the church of Saint Sulpice, 
in London it has been found in large quantities in iron 
in Paris; they weigh five hundred pounds, are ihore than 
water pipes, encrusted with a ferruginous deposit. On 
two feet across, and were presented to Francis I. by the 
the Continent it is found in the Wolga, Danube, Elbe, 
Republic of Venice. Specimens attaineven largerdimen- 
and many of the rivers of Germany and Belgium. 
sionsthan these, and indeed are, without exception, the 
Passing over the genus Galeomma, we come to the 
largest shells known. The byssus is so large, and its 
Clam Shells. 
attachment to the rock so strong, that it is frequently 
necessary to cut it with a hatchet, in order to remove 
the shell. The animal is good eating, and some of our 
Fa M ILY— TRID ACNID^. 
earlier voyagers have mentioned it as furnishing their 
sailors a wholesome meal. Captain Cook states that 
The Clam Shells are solid, opaque, white shells. 
they sometimes weigh upwards of twenty pounds; and. 
regularly equivalve, truncate anteriorly. The v^alves 
as Mr. Broderip observes, “a fine well fed Indian giant 
are strongly ribbed externally, and the margins dentate 
Tridacna would furnish forth a dish for a dozen.” The 
internally. The ligament is external, and the hinge is 
genus is figured in Plate 10, fig. 8, by Tridacna crocea. 
furnished with very oblique, interlocking teeth. The 
Genus Hippopus, Horse-hoof shell, or Bear’s-paw 
Clam Shells are the giants among the Bivalves, and 
Clam. — This genus has a transversely ovate shell of 
live attached by their byssus to rocks, shells, and corals. 
moderate size, ribbed, and squamous externally. It is 
“They also have the faculty of foimiing holes in the 
readily distinguished from the .preceding by its valves 
surface of the shell or coral to which they may happen 
being closed and flattened in front, and, in consequence. 
to be fixed.” — {Gray.) 
baving no aperture for a byssus, and by having only 
Genus Teidacna. — T his genus has a massive 
two compressed cardinal teeth in each valve. The 
trigonal shell, ornamented with radiating ribs and 
only known species, H. macidatiis, is a handsome shell. 
imbricating foliations. The valves have a wide gape 
white, spotted with red or purple, and is found on the 
close to the beak in front, occupying nearly the whole 
coral reefs of the Indian Ocean. The shells are now 
anterior side, for the passage of the large byssus. The 
much used in the ornamental arts, for making into ink- 
hinge is composed of a single cardinal, compressed. 
stands and other useful purposes. 
Order II. PHOLADACEA. 
In this order’ the animals have in general a closed 
is very deep. The animal is symmetrical, club-shaped. 
mantle, with two more or less elongate siphonal tubes. 
or worm-like; the mantle is closed in front, except the 
which are almost always united. The gills are pro- 
orifice for the passage of the foot, which is club-shaped 
duced behind into the inhalent or lower siphon; and 
and truncated ; and the siphons are large, elongated. 
the foot is frequently more or less elongated and club- 
and united nearly to the ends. The Pholades are found 
shaped. 
in most parts of the globe, and all the members of the 
Family— PHOLADIDA l. 
tribe are borers into stone, clay, wood, or other sub- 
stances. The species are numerous, are widely dis- 
The Pholades have a thin, white, brittle, and exceed- 
tributed, and they may even be said to be cosmopolitan. 
ingly hard shell, with the valves united only by a very 
The question how the boring mollusca excavate tbeir 
thin ligament, gaping at both ends, and armed with 
dwelling-places has been the subject of much discussion. 
rasp-like imbrications in front. The shells are either 
and is still in a great measure undecided amongst 
free or within a shelly tube. The hinge is without any 
Naturalists. 
cartilage, and has no teeth, but is often strengthened 
Pholadina. — T he true Pholades have an elongated 
externally by accessory valves. The hinge plate is 
cylindrical shell, with the anterior gape either open 
reflexed over the beaks, and is furnished with a long, 
or, in the adult, closed by a callous plate, and the 
curved muscular process beneath each. The pallial sinus 
dorsal margin covered by accessory valves. The 
