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F.CHINODEKMATA. 127<br />
the ossicles have diminished in proportional thickness while increasing<br />
in length, and so having lost their earlier stoutness, now<br />
require external aid; and (c) a final condition, in which equilibrium<br />
is again established, the ossicles themselves being again stouter,—or<br />
whether we have to do with two sets of variations from a common<br />
stock, due to some slight differences in the environment. But this<br />
is a complex and difficult question, which can only be satisfactorily<br />
answered by one who has at hand the living wealth of the Aus-<br />
tralian seas.<br />
Port Curtis ; Fitzroy Island ; Albany Island ; Port Denison,<br />
8-12 fms.<br />
10. Linckia, sp.<br />
A very small specimen, from West Island, Torres Strait, presents<br />
that interesting peculiarity of three smaller and three larger arms,<br />
hinting thereby at a division of the disk instead of gemmation from<br />
a single arm; it is the smallest heteractinic Lmclcla I have seen, the<br />
longest arm measuring only G millim.<br />
Perrier, p. 276.<br />
11. Anthenea flavescens.<br />
Port Jackson, 0-5 fms.<br />
The Museum collection contains also specimens of this species<br />
from Fremantle, W. Australia.<br />
12. Oreaster gracilis.<br />
Pentaceros gracilis, Perrier, p. 246.<br />
Oreaster gracilis, Liitken, Vid. Med. 1871, pp. 260, 261.<br />
A selected series of five specimens, all from Port Denison (4 fms.),<br />
exhibit remarkably well the great change which occurs in this<br />
species, even after a considerable size has been attained. The<br />
smallest, which has E, equal to 93-5 millim., has five tubercles,<br />
about 10 millim. high, one at the central end of each median row<br />
of tubercles : in another, with R equal to 108 millim., the<br />
tubercles, though a little stronger, are no higher and are here only<br />
to be found on three of the angles of the disk ; this specimen, like<br />
another which is a little larger, has the lateral and marginal spines<br />
very well developed: two specimens, with P equal to 118 and<br />
140 millim, respectively, have these spines less well developed, and<br />
the diminution is the more marked in the larger specimen ; the<br />
smaller has one large central tubercle, and the larger has each of<br />
the whole set of five reduced to growths which are hardly larger<br />
than the other spines on the disk.<br />
A specimen with six arms, one of which has been injured and<br />
has commenced to grow again, was collected at Port Molle.
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