long, the creature is formed on precisely the same principle as the Piddock.
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At the upper extremity, and just at the spot where the siphons begin to diverge from each other, are a pair of remarkable projections, technically named "pallets," which are of various shapes and sizes, according to the species which forms them. In the commonest British species, Teredo norvagica, they are of shell, and simple in their form, as may be seen in the accompanying illustration, fig 5. In others they are of more elaborate structure, as, for example, in Teredo bipennata, where they are horny in texture, and shaped something like feathers, as may be seen at fig. 1, which represents a single valve of the shell and the pallets lying behind it. Fig. 2 represents the same portions of Teredo palmulata, in which the pallets
