EXPLANATION OF THE PARTS OF SHELLS. 
MULTIVALVE. 
A muttTivatve shell is composed of more parts than two. 
Every part of a shell which is connected by a cartilage, ligament, 
hinge, or tooth, iscalled a valve of such shell; thus, the Chitens 
have eight transverse, broad, but very short valves, placed on the 
back of the animal, and inserted at their sides into a marginal 
tough ligament. Platel. fig. 1l,aaa. 
Operculum consists of four small valves on the summit of the — 
Lepas, which shut up the superior orifice ; it is in a certain degree 
stationary, and different from the operculum of univalve shells, 
which will hereafter be described. Plate I. fig. 1,4. Fig. 9 re- 
presents a profile view of the operculum removed from its place, 
a the front valves, 6 the back valves. Fig. 10 a front view of 
the operculum. ; 
Base is that part of the shell by which it is fixed to rocks and 
other bodies. Plate I. fig. 1 and 2,8 8 B.—nisa piece of stone 
to which the base is fixed, and e& a piece of wood to which the 
shells of this section are generally attached. 
Ligament is the membranous or tendinous substance by which 
the valves or parts of the shell are attached. Some multivalve 
she]ls are connected by the parts of one valve locking into 
another. Plate I. fig. 2,» p p. The ligaments vary considerably 
in their texture, being scaly, prickly, smooth, or punctated. 
Ridges are certain convexities in many of the Lepas tribe, 
sometimes longitudinal and sometimes transverse. Plate I. fig. 1, 
FF. 
Peduncle. A sort of stem by which the shells of the Anatifera 
are attached to wood, &c. It is a membranaceous substance, 
similar to a bladder but materially thinner, and filled with a liquid 
which evidently affords nourishment to the animai. Plate I. fig. 
2,c c; the peduncle is usually affixed to a piece of wood as re- 
presented at c. 
