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bristling with spines on the upper part, and alive with myriads of suckers below. Then we have the true types of this class in the Sea Urchins, or Sea-eggs, covered with spines—purple in colour,—most exquisitely fluted, and with a rim at the base of each regularly crenated. There are few who gather the denuded, so called shell of this animal as it is thrown up on our shores, would own the relationship between them. And such jaws as they have, with which our own cannot compare for one moment; here now is a specimen before us from which we have extracted the whole dental apparatus,—it is, to own the truth, the first time we have so carefully observed it. In the living animal merely the five triangular teeth closely fitting together can be noticed, and we were scarcely prepared for the large jaws in which we found them. These jaws are, as the teeth, five in number, and form a five-sided cone, and in a socket passing through each the teeth are imbedded; when examined separately, they are found to resemble in figure a triangular pyramid, the external surface being smooth, with eminences for the attachment of muscles, whilst the other two sides are flat and marked with groovings resembling a very fine file. When fitted together, these grooved flat sides of each jaw are in apposition with the corresponding surface of two others, so that there are in fact ten grinding surfaces formed, between which the food must pass preparatory to its introduction into the digestive canal. The food of the Echinidæ consists of shell fish, but in an allied family the Spatangideæ or Heart Urchins, some magnificent fossil specimens of which we took some years since from
