520 
MOLLTJSCA. 
TUBE OF THE PEEFORATED 
A BLOCK OF STONE PEHFOBATBD BT THE PHOLAS DACTYLU8. WATERING-POT SHELL. END OF TUBE MAGNIFIED. 
ORDER 1. SIPHONATA. 
THE SHIP-WORM. 
This terra is derived from tlie Greek siphon, a curved tube. It includes several remarkable 
species. Among tbem is the Wa- 
tering-pot Shell, jispergillum 
vaginiferum: the animal in this 
case is inclosed in a calcareous 
tube, the anterior extremity of which is closed by a curious perforated disk ; the other end is 
ornamented with several ruffle-like bands. To this family belong the Pholaclidce, the species of 
which are noted for boring into hard substances, some of them 
making their burrows in limestone rocks, and others in wood. 
One of the most celebrated species is the Ship-Wokm, Teredo 
navalis, a small, worm-like animal, which bores into wood sub- 
merged in sea-water, and often does great damage to ships, and 
to piles used for wharves and breakwaters. They bore perpendic- 
ularly, and often in great numbers, but they never encroach upon 
each other. "When stretched out they are one to two feet long. 
Metal sheathing and broad-headed iron nails bave been found 
to be the best defense against these destructive pests. 
THE VENERACEA. 
These constitute a tribe of bivalve moUusks with elongated 
siphons, and include many very elegant shells ; they generally 
conceal themselves by burrowing, sometimes in the sand and mud, 
and sometimes in the solid rock. The principal agent in these 
operations is the foot. One of the most remarkable species is 
the Cytherea dione, the posterior border being beset by spines, 
and the sides farrowed with elevated lamellse. The color is of 
a beautiful rosy purple. Found in South American seas. The C. 
convexa is a small species, one inch and a half long, found on muddy 
bottoms along our coasts from ISTew Jersey to Mexico, and is called He-Clam by the fishermen. 
THE CYTHEREA DIONE. 
