BIVALVES—SOLEN. 19 
SOLEN.—Razor-sHEATH OR KNIFE-HANDLE. 
DESCRIPTION OF PLATE V. 
Dy. I. —Fig. 2. S. truncatus. Drv. I].—Fig. 4. S. vespertinus. 
Fig. 3. S. vagina. Fig. 5. S. radiatus. 
Dr. I].—Fig. 1. S. oriens. Fig. 6. S. occidens. 
Shell bivalve, oblong, open at both ends: hinge with a subulate re- 
flected tooth, often double, and not inserted in the opposite valve. 
OF this genus there are thirty-five species, which 
vary exceedingly in form and general appearance. 
The principal characteristic is derived from the 
hinge, usually supplied with one subulate tooth, 
which is often found double, though not always 
inserted in the opposite valve. 
Most species of the Solen are covered with a 
thin cuticle or epidermis, which renders the colors 
beneath more or less obscure. 
The first division consists of those species, whose 
breadth greatly exceeds their length; and the second, 
of those that are oval or oblong. 
In some species of the first division, as in S, siliqua 
S.vagina, &c. the breadth of the shell is nearly seven 
times its length, giving it a resemblance to the handle 
of a knife, or sheath of a razor; and some are curved 
or bent like the scabbard ofa scimitar. The shells 
of this division have both ends invariably open. 
The greater proportion of the shells of this genus 
are found in the European and Northern seas. The 
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