62 ZOOLOGY. 
branches, where they may be seen suspended at low tide. There are four 
lanceolate labial palpi; and the branchize, two upon each side, are 
conspicuous objects when the shell is opened.. The very large liver is 
recognised by its dark color, which causes it to be indistinctly seen through 
the translucent integuments. There is no appearance of a rudimentary foot, 
but eyes have been detected. 
The ancient Romans were very fond of oysters, and soon discovered 
those of Britain to be superior to their own, and imported them in winter 
packed in snow, and in such a manner as to prevent the valves from 
opening, a mode still practised when oysters are to be transported a 
considerable distance. Previous to this period Sergius Aurata had invented — 
and practised the art of breeding oysters in artificial beds, turning his art to 
great profit. This is still practised in the Mediterranean, where ponds are 
used, into which the sea enters at high tide. About Naples oysters attach 
themselves to sticks, and here numerous poles are stuck into the bottom, 
and when the oysters which become affixed to them have acquired a 
sufficient size to be taken, they are collected by withdrawing the poles. 
Oysters attain a marketable size in four or five years, although not yet fully 
grown, large individuals being considered less delicate than those of a 
medium size. Those are most highly esteemed which have grown in the 
mouths of rivers, where the water is less saline, and it is probable that their 
food varies according to the locality. Oysters feed upon infusoria; and 
when certain green kinds are abundant, they impart a green color to the 
animal, a color which is often incorrectly attributed tosome mineral 
substance. The extent to which oysters are consumed would exterminate 
them in accessible localities were they not prolific. A single oyster 
may eject 50,000 or 60,000 eggs in a year, commencing in the spring and 
continuing through the summer. | 
Deshayes does not think the genera Gryphea, Lamarck, and Hzogyra, 
Say, are sufficiently distinct from Ostrea; whilst Von Buch, the celebrated 
geologist, insists that they are founded.upon good characters. The former 
author is inclined to look for variations in the soft parts of allied genera, 
although in such the shell usually presents the more prominent generic and 
specific characters. Variations in the shell are as important among the 
Mollusca as in the teeth and horns of the Mammalia, or the bill and feathers 
of birds ; and, although a species may be found which associates it with two 
genera, this is not sufficient evidence that the two should be united. 
According to Deshayes, Ostrea passes by insensible gradations into 
Exogyra, and this, by equally gradual steps, returns to Ostrea, so that in 
his opinion the species of the three form but one natural genus. 
Fam. 4. Pectinide. In Pecten (pl. 76, figs. 27 to 29), the chief genus 
of the family, the shell is regular, toothless, inequivalve, eared at the hinge 
margin ; ligament entirely internal, and placed in a triangular depression ; 
surface often covered with ribs. Mouth with deeply cut lips and a pair of 
palpi on each side; mantle disunited, margin with numerous cilia, having 
eyes between them ; branchiz sub-divided into separate parallel filaments ; 
foot small and dilated, a byssus sometimes present. The genus Pecten is 
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