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71 purpose distinguishing our Australian species under the sub-generic name of Monaster} The genus Urasterella, McCoy, 1 2 likewise only possesses the adambulacral plates on the ventral surface ; hut in this case neither are there marginal plates, so far as I can glean from Sir P. McCoy and the late Professor Porbcs’s descriptions. P alas aster (Monaster) Clarkei, Dc Koninck. PI. XIY, Pigs. 1 and 2 ; PL XV, Fig. 4. Palceaster Clarkei, Do Koninck, Foss. Pal. Nouv.-Galles du Sud., Pt. 3, 1877, p. 1GG, t. 7, f. 6, G\ Sp. Char.—Body large, shortly stellate, robust; disc large, strongly pentagonal, raised above the level of the tumid rays, straight walled, surface flat, or a little concave, hearing five tubercles. Bays broad, thick, and tumidly petaloid; margins convexly curved ; abactinial surface arched; actinial surface flat or somewhat concave; intcrbrachial areas sharply V- slxaped. Abactinial plates hexagonal, thick, and convex, arranged in three rows, eight to ten in a row, the median the smallest, and alternating with the lateral series, which are transversely elongated. Ambulacral avenues rather broad and elongately petaloid, gaping, and deep; ambulacral plates small, and apparently in two rows. Adambulacral plates eighteen to twenty in a row, large, very transverse, narrow, and convex. Marginal plates subdorsal in position, convex, narrow, and triangular, more or less resembling the plates of the abactinial surface, hut differing in ornament. Madreporiform plate large, oval, situated on the straight Avail of the disc. Oral plates not pre served. Ornament of plates tubercular, the abactinial ray plates being covered with densely packed small granules radiately arranged, hut the marginal plates hear large tubercles, which carry short, fine, projecting spines. / Ohs.—There is doubtless much truth in the late Prof, dc Ivoninck’s statement that P alee aster Clarkei is one of the largest of theknoAvn Palaeozoic starfish; hut that it is not the largest is shown by comparison with the tAvo succeeding species, nor does P. Clarkei precisely resemble any species of the genus Avitli which I am acquainted. 1 From the one or single row of adambulacral plates on each side of an ambulacral avenue. 2 Brit. Pal. Foss., 1851, Fas. I, p. 59. Stenaster, Billings, is generally said to be identical with this. (Hall, Loc. cil., p. 289.) 11a G1—92 C