Now some of the true testacean have shells in more than one or two pieces, and therefore this last explanation of the term is rather calculated to mislead a learner; but we shall explain presently wherein the difference consists between them, and the CRUS-TA-CE-OUS, or, as we pronounce it, _krus-ta-shus_, fish consists. Here is another long word, it comes from the Latin _crusta_, a word of many meanings, all having reference to an outer coat or covering. My readers know all about pie-crust, and have perhaps heard a surly, snappish, peevish person called a crusty fellow; they will now understand what is meant by a _crustacean_ and _crustaceology_, that part of Zoology which treats of crustaceous animals. They constitute quite a large family, these _ologies_, and have a strange way of twisting themselves about, and exchanging limbs and features, so that one is puzzled at times to tell which is which. But here we have fixed two of them, called TESTACEOLOGY and CRUSTACEOLOGY, twin brothers, and very much alike in their characteristics. Let us have a good look at them, so that we may know them again if we should lose sight of them for awhile. Now we will spell over the name of the first— CONCHOLOGY. Why, it is changed already? Has this science of shells then another name? Yes, and this is it, pronounced _kong-kol-o-gy_, and derived from the Latin _concha_, which means properly a shell-fish with two shells, joined by a hinge, as the oyster, the cockle, etc. This present volume then is a work on _Conchology_, the subject of it is _Conchiferous_, and whoever studies it will be doing something towards becoming a _Conchologist_. So much for names and titles; but still we have the question to answer, What are shells? In a learned work called a Cyclopædia, we find it stated that “shell is the hard calcareous (that is chalky) substance which protects, either partially or entirely, the testaceous mollusks externally, or supports certain of them internally.” All this you will understand, except perhaps the word ‘mollusks;’ this is a term applied to soft-bodied animals, such as shell-fish, snails, etc., about which we shall have more to say as we proceed. By this we learn that _all_ shells are not external or outer coverings, some are internal or inner supports for the soft, jelly-like bodies to which they belong, thus performing the duty of bones. An example of this is seen in the shell of the Cuttle Fish, called by naturalists _Sepia_, a description of which will be found further on in the book. Shells are either _Crystalline_ or _Granular_. Now look at those two words, they almost explain their own meaning. Crystalline shells are those which have more or less of clearness, transparency as we say, so that if held against the light it shews through them; they are sometimes called _Porcellaneous_ shells, from their resemblance in this respect to porcelain, or chinaware; the Common Cowry, (_Cypræa Tigris_,) is a shell of this description.