“And yet, my dear, if you had wished to find this shell, and place it among your collection, the name by which I called it would have been of little assistance to you; for there are other small purple shells, which you might very likely have mistaken for the one in question: and, perhaps, the first person you asked about it, would have told you it was something quite different. Had you been in a foreign land, the English name would have been useless; and, indeed, even in various parts of our own country, things are called by very different names. The object is to find an appellation for it, and other shells, which shall be common to all naturalists; and thus assist you, by reference to their works, to discover every thing that is known respecting them. The shell we have been speaking of, is the _helix janthina_; and when once you are acquainted with this, its Linnæan name, you may readily find, in books on conchology, such a description of it as would prevent your mistaking any other for it. I believe you already know the three great divisions into which shells are arranged, of _univalves_, _bivalves_, and _multivalves_.” “Yes, mamma,” said Lewis, taking up a common whelk, (_buccinum_,) “this belongs to the first division; it has only one piece.” “And this muscle,” said Edward, “is a _bivalve_. I do not see a _multivalve_ in this collection.” Mrs. Ashton soon found one. “Now, mamma,” said Lewis, “before you tell us the name, will you show me how to set about finding it for myself?” “Willingly,” said Mrs. Ashton; “it is always pleasant to help those who try to help themselves: but in this instance perhaps Edward will lend his assistance; and I shall then have the additional satisfaction of knowing that he does not forget what he has once learned.” “Mamma taught me,” said Edward, “that there are but three classes in the _multivalve_ division of shells; and this you see must belong to one of them, for it has many pieces. Now, Lewis, I will read to you what my text-book says about them; and you shall see which description answers best to the shell we have been looking at. First, the _chiton_, canoe or boat-shell, consisting of several segments, placed transversely, and lying upon each other at their anterior edge.” Lewis put on a considering face, and again examined the shell. “Let me see,” said he, “segment—that means part of a circle, placed transversely—cross-ways, and lying one over the other. I see nothing of the kind: besides, this is not at all in the shape of a boat or canoe, so it cannot be a _chiton_.” “Will you go on to the next class, if you please?” “I have not finished the account,” said Edward; “but, since you are so well satisfied, we will try the _lepas_, or barnacle.” Edward reads:—“Shell affixed at the base; and consisting of many unequal erect valves.”