71 
purpose distinguishing our Australian species under the sub-generic name 
of Monaster} The genus Urasterella, McCoy likewise only possesses the 
adamhulacral plates on the ventral surface ; but in this case neither are there 
marginal plates, so far as I can glean from Sir P. McCoy and the late 
Professor Porhes’s descriptions. 
PAL.EASTER (MoNASTEii) Clahkei, De Konincl', 
PI. XIV, Pigs. 1 aud 2 ; PI. XV, Pig. 4. 
Palceaster Clarkei^ De Koninck, Poss. Pal. Nouv.-Galles dll Sud., Pt. 3, 1877, p. lOG, 
t. 7, f. 6, 6". 
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, bearing five tubercles. Piays broad, thick, and 
tumidly petaloid ; margins convexly curved ; abactinial surface arched ; 
actinial surface flat or somewhat concave ; interbrachial areas sharply Y- 
shaped. 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 resemliling tlic plates 
of the abactinial surface, but differing in ornament. INIadreporiform plate 
large, oval, situated on the straight wall of the disc. Oral plates not pre- 
served. Ornament of plates tubercular, the abactinial ray plates being 
covered wdth densely packed small granules radiately arranged, but the 
marginal plates bear large tubercles, wdiich carry short, fine, projecting spines. 
Ohs. — There is doubtless much truth in the late Prof, de Koninck’s 
statement that ^aleeaster Clarkei is one of the largest of the known Palseozoic 
starfish ; but that it is not the largest is shown by comparison with the two 
succeeding species, nor does P. Clarkei precisely resemble any species of the 
genus with which I am acquainted. 
1 From the one or single row of adamhulacral plates on each side of an ambulacral avenue. 
^ Brit. Pal. Boss., 1851, Fas. I, p. 59. StenaMir, Billings, is generally said to be identical with this. 
(Hall, Loc. cil., p. 289.) 
11« G4— 92 
C 
