derives its name of arctica from the fact that it is more common on the northern than on the southern coasts, thus reversing the habits of the preceding species. As, therefore, I have called the preceding species the Rough Stone-borer, I will designate this animal the Northern Stone-borer, both names being little more than translations of their accepted scientific titles.
It is found at various depths, but hides itself so cunningly that a casual observer would not notice it. If the reader should be able to manage a dredge, he will be nearly certain to find some specimens of Saxicava arctica, provided that he knows where to look for them. When the dredge hauls up a quantity of the large sea-weeds, search should be made among the roots, and in many cases the shell of the Northern Stone-borer may be found deeply imbedded in them. Sometimes it is hidden in masses of still living zoophytes, sometimes it is concealed among oyster-shells, and in many cases it is sunk so deeply .into a tuft of growing coralline, that its presence would not be suspected until the plant was torn asunder.
It is a small species, the average length of the shells being half an inch.
We now pass to the second Plate, in which are depicted a number of curious and interesting species.
In the upper left-hand corner is represented a shell called Petricola lithophaga, which we may venture to term the Rock-shell. Although this is not in itself an especially rare shell, it is not plentiful in England, is exceedingly scarce in cabinets, and anyone who possesses a specimen in tolerable preservation may think himself exceedingly fortunate. As its name implies, it buries itself deeply in the rock, respiring and obtaining nourishment by means of the siphons, which are separate and rather radiating from each other.
Foreign specimens of this shell are plentiful enough, as it is common in the Mediterranean, and abundant
