127 
ASTEEOIDEA. 
PAL^ASTEH, J. Hall. 
Pal^aster Clarkei, L. G. de Konincle.^ 
PI. VII, Fig. 6. 
The size of this species surpasses that of all the species of Palaeozoic 
Asteroidea yet known. Its rays measure not less than five centimetres from 
the centre of the disc to their extremities ; they are very thick, and joined 
to each other for about half their length ; the angle formed by the marginal 
sides at the extremity of each ray is about 75° ; their dorsal surface is com- 
posed of three rows of strong transverse plates, of a sub-hexagonal form, 
closely united, and covered with a considerable number of small tubercles, of 
which the greater part are rounded, and resemble the jolates of JPalce- 
chinus elli'pticus and P. sphericus, Scouler, while some are only pointed and 
look like little spines ; these last are nearly all marginal. The covered portion 
of the disc is, unfortunately, in too bad a state of j)reservation to allow me to 
see its exact structure ; it appears analogous to that of Palceaster matutina. 
Hall, and I observed in it one plate bearing in relief a starred tubercle. The 
marginal plates have nearly the same width as the principal adjacent plates, 
but they are only half as long, and, consequently, much more numerous ; 
they differ from the central plates by the presence, on their anterior edges, of 
a row of large pointed tubercles, numbering five or six for each plate. 
The ventral surface shows a strong ambulacral groove, bordered at 
each side by sixteen or eighteen ambulacral plates of unequal width, present- 
ing altogether a petaloid appearance. The ambulacral plates are very much 
wider than long, thin in the direction of their length, and arched in that of 
their breadth ; their surface is ornamented with an infinity of small granules, 
visible to the naked eye ; they terminate at the side of the disc by a small 
auxiliary plate rounded and tuberculiform. It was impossible for me to see 
exactly the shape of the mouth or of the small plates which surround it. 
It must be observed that the marginal plates are distinctly visible from the 
dorsal side, presenting the appearance of a supplementary series of plates on 
each side of the ray, joined to the three normal series of which it is composed. 
' [Palceaster [ilonaster) Clarkei. — R. Etheridge, Junr., Mem. Geol. Survey N.S. Wales, Pal. V, p. 2, 
1892, p. 71, pi. 14, figs. 1, 2, pi. 15, fig. 4.— W.S.D.] 
