N. ZOOL. GAL.] NATURAL HISTORY. 157 
the part of the body near the head of the animal, and 
which is always inclosed in a case or hard skin. This 
skin has an opening at the end of the free part for 
the passage of the fringed feet, which, by their action, 
create a current to carry the small animals, in the sea, 
near the mouth placed at the base of the cavity. The 
edge of this opening in the case, is always furnished 
with four, more or less, distinct valves, and the base 
of the case is generally surrounded with other similar 
valves ; the animals are divided into families and ge¬ 
nera according to the developement of these valves. In 
the Sea Acorns, ( Balanus ,) the four valves, (usually to¬ 
gether called the operculum,) are nearly equal sized, and 
sunk into a flexible skin, which allows them to move in 
the cavity formed by the (four, six, or eight) valves which 
surround and inclose the base of the body. These latter 
valves are united together side by side by a dentated 
suture into a bell-shaped body, and they are increased in 
size (as the animals grow) by the addition of new matter 
to the base and outer side of each of the valves, deposited 
by the processes of the skin, which are placed for the 
purpose between their sutures. They are generally affixed 
to wood and stones, but a few attach themselves to the 
bodies of whales, and as they grow and their shells are 
enlarged by the addition of new matter to the base of the 
valves, they gradually raise themselves out of the sub¬ 
stance of the skin, in which they were immersed in their 
young state. Some of the genera which live in this 
manner, as the Coronula , to enable them to hold more 
firmly to the skin, form a shell which is variously 
folded on its edge, the folds being refolded, and thus in¬ 
creasing in number as the shell enlarges in diameter. 
These shells are greatly altered in form according to their 
position; if they are separate they are broad and expanded, 
if crowded they are narrow and high. In Balanus it is 
the case that is lengthened, and in Clurona it is the valves 
that are produced and altered in shape. 
The Barnacles or Goose-shells, ( Lejpas ,) as they have 
been called, from the extraordinary belief that they were 
the origin of the Barnacle geese, have a compressed 
body, which is placed on a long pedicle arising from be¬ 
hind the head of the animal. This pedicle is sometimes 
