EXPLANATION OF THE PARTS OF SHELLS. 13 
Seam. When the valves are closed, the line of separation 
between them is so called. Plate II. fig. 6, ¢ ¢. 
Umbo. That partsituated immediately under the deak. Plate. 
fig. 6, w; and Plate Il. fig. 4, w. 
Ears. The processes on each side of the beak,in most species 
of that division of Ostrea, called Pecten ; some have one ear very 
large, and the other small; and some are scarcely observable on 
one side. Pl. II. fig. 2, h A. 
Superior Ear. Plate IV. fig. 11, h. 
Inferior Ear. Do. doe” n= 
Margin. 'The extreme edge of the whole shell, or the circum- 
ference of either valve, allround. Plate I. fig. 4, #; and Plate II. 
rg ay 
Crenulated margin. That fine notched edge of shells, which 
unite into notches in the opposite valve, as genus Donax. Plate 
IV. fig. 6, m 1m. 
Striz are fine thread-like lines, generally on the exterior surface 
of shells, and are sometimes both longitudinal and transverse. 
When the strie of shells appear indistinct, as if worn out, it is 
termed obsolete striz. In some instances the insides of shells are 
striated; for example, the Fasciolaria Tulipa. The character of 
the strie is often of much use in distinguishing species. Plate II. 
fig. 2, f 
Right Valve is that valve which, when viewed with the inside 
uppermost, has the anterior slope pointing to the right hand. 
Plate I. fig. 8; and Plate IV. figs. 5 and 6, B. 
Left Valve. The opposite of the above; the anterior slope 
points to the left hand, when viewed from the inside. Plate IV. 
figs, 3; G; 7,9, &c. : 
Length of the Shell is taken from the ligament, or the beak, to 
the opposite margin. For example, Mytilus: it is longer than it 
js broad, and the Solens are broader than long. Plate I. fig. 5, 
uu; and Plate II. fig. 4, v v. 
Breadth is measured from the most extreme edge of the ante- 
rior and posterior slopes, being in a contrary direction from its 
length. Many shells are broader than long, such as most of the 
Mye, Solene, Telling, &c. ; and the Mytilus, Ostrea, Pinna, &c., 
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