I have already in a previous article named the different Orders of this Class in their relative rank, and have compared the standing of the living ones, according to the greater or less complication of their structure, with the succession of the fossil ones. Of the five Orders, Beches-de-Mer, Sea-Urchins, Star-Fishes, Ophiurans, and Crinoids,--or, to name them all according to their scientific nomenclature, Holothurians, Echinoids, Asteroids, Ophiurans, and Crinoids,--the last-named are lowest in structure and earliest in time. Cuvier was the first naturalist who detected the true nature of the Crinoids, and placed them where they belong in the classification of the Animal Kingdom. They had been observed before, and long and laborious investigations had been undertaken upon them, but they were especially baffling to the student, because they were known only in the fossil condition from incomplete specimens; and though they still have their representatives among the type of Echinoderms as it exists at present, yet, partly owing to the rarity of the living specimens and partly to the imperfect condition of the fossil ones, the relation between them was not recognized. The errors about them certainly did not arise from any want of interest in the subject among naturalists, for no less than three hundred and eighty different authors have published their investigations upon the Crinoids, and the books that have been printed about these animals, many of which were written long before their animal nature was suspected, would furnish a library in themselves. The ancients knew little about them. The only one to be found in the European seas resembles the Star-Fish closely, and they called it Asterias; but even Aristotle was ignorant of its true structural relations, and alludes only to its motion and general appearance. Some account of the gradual steps by which naturalists have deciphered the true nature of these lowest Echinoderms and their history in past times may not be without interest, and is very instructive as showing bow such problems may be solved.