NATURAL HISTORY, 
142 
[east. zool. 
a more or less developed foot; the cartilage is placed 
in a small triangular internal pit. 
The family of Pectinidce have rather a large foot, which 
enables the animal to move about, and they have a tuft of 
byssus at its base, which passes out at a notch under the 
front margin of the right valve, by which they affix them¬ 
selves to rocks and other marine bodies, like the Muscles. 
The dorsal edges of the valves are produced at each side 
into ears. The Pectens have small bright eyes like spots 
on the edge of the mantle, which are not found in the 
Limce. 
The family of Spondylidce have a small foot without any 
byssus, and the shells are attached to rocks and stones 
by the outer surface of one of the valves. In Spon- 
dylus and Plicatula , the hinge margin is provided with 
two large interlocking teeth in each valve, and in Hinnites 
the hinge is toothless like the Pectens , with which it has 
generally been confounded. 
The remainder of these animals have lamellar shells 
and no foot. 
The family of Oysters ( Ostreidee ) have a thick iaminal 
shell, and the animal has short lips, separate from the 
gills ; they live attached, like the Spondyli , by the outer 
surface of their shells; the cartilage is placed in a large 
triangular internal pit. 
The family of Placiinidce are very peculiar for having 
a very compressed body and thin nearly transparent 
shells ; the cartilages are placed on the edge of two di¬ 
verging ridges on one of the valves, which fit into two 
grooves in the other. These shells are sometimes used 
as glass to glaze windows. 
The family of Anomiadce have the thin pellucid shell 
of the former, but the body is usually rather more convex, 
and they are attached to marine bodies by a peculiar mus¬ 
cle, which passes out through a notch in front of, one of 
the valves; this muscle after a time secretes on the sur¬ 
face to which it is affixed a stony substance, formed of 
longitudinal shelly plates, probably deposited between the 
fibres of the muscles, which has been called a stopper, and 
by some considered as a third valve. In Anomia this 
stopper is free. In Placunonomia it is fixed in the notch. 
