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same difficulties which we have felt in selecting from other grand Divisions of the animal kingdom, subjects of comparison between the extinct and living forms of their respective Classes, Orders, and Families, embarrass our choice also from the last Division that remains for consideration. Volumes might be filled with descriptions of fossil species of those beautiful genera of Radiated Animals, whose living representatives crowd the waters of our present seas.

The result of all comparisons between the living and fossil species of these families would be, that the latter differ almost always in species, and often in genus, from those which actually exist; but that all are so similarly constructed on one and the same general Type, and show such perfect Unity of Design throughout the infinitely varied modifications, under which they now perform, and ever have performed the functions allotted to them, that we can find no explanation of such otherwise mysterious Uniformity, than by referring it to the agency of one and the same Creative Intelligence.

animals that compose this highest Class in the grand division of Radiated animals, viz. Echinidans, Stelleridans, and Crinoïdeans, have, till lately, been considered as made