No. 14. OSTREA. 



Oyster and Scallop. Inhabitant a Tethys. 



Shell bivalve, generally unequal valves, and slightly eared hinge without 

 teeth, furnished with an ovate hollow, and mostly lateral, transverse furrows; 

 " Vulva unusque nullus," Linnaeus; these are divided into three families; valves, 

 radiated and eared, as in the Pectens; rugged and rough, as in the Oedulis; 

 hinge with a perpendicular, furrowed line, as in the species Perna, and iso- 

 nogmon. The Pectens are again subdivided into three sections, viz., those 

 with the valves inequilateral, and the ears equal; those with the ears unequal, 

 and having one of them ciliated, with spines within; and those with the 

 valves gibbous one side: the two other families are not subdivided. The 

 difference between the Pecten and the Oyster tribe is so obviously impressed 

 by the hand of Nature, on the respective shells which compose them, that 

 kw writers on this subject have passed over silently the impropriety of 

 placing them together. As Linnaeus considers the animals which inhabit the 

 Scallop and Pecten as the same, and describes them as a Tethys, it may not 

 be improper to speak more fully on this subject. 



The Scallop differs from the Oyster, the animal having the branchiae cirra- 

 ted or fringed, in being furnished with a kind of foot, which it protrudes from 

 the shell near the article of the hinge, and of throwing abiscus, like the pinna 

 and the muscles, by which it affixes itself to other bodies. 



The Ostra has the branchiae simple and not fringed, and is unfurnished, 



ther with a foot or with byssus, and its powers of motion consist in turning 

 idler the flat or the convex side upwards or downwards; and even to effect 

 this, the animal takes the advantage of the ebbing or flowing of the tide to as- 

 sist it. See Lister on Scallop, P. T. 1st vol. 



Eighty species of this genus are at present known. 



In Lamarck's arrangement, the two genera, Huitre Ostraea, and Pieque Pec- 

 ten are retained; but four other genera are constituted under the names of Gry- 

 phus, the Ostraea Gryphus of Linnaeus, a shell as yet found only in a fossile 

 state. The most remarkable species of oyster is the Ostraea Malleus, or 

 Hammer oyster, which resembles a pick-axe, and is (particularly the white 



