Report on the zoological collections made in the Indo-Pacific Ocean ...

F.CHINODEKMATA. 127the ossicles have diminished in proportional thickness while increasingin length, and so having lost their earlier stoutness, nowrequire external aid; and (c) a final condition, in which equilibriumis again established, the ossicles themselves being again stouter,—orwhether we have to do with two sets of variations from a commonstock, due to some slight differences in the environment. But thisis a complex and difficult question, which can only be satisfactorilyanswered by one who has at hand the living wealth of the Australianseas.Port Curtis ; Fitzroy Island ; Albany Island ; Port Denison,8-12 fms.10. Linckia, sp.A very small specimen, from West Island, Torres Strait, presentsthat interesting peculiarity of three smaller and three larger arms,hinting thereby at a division of the disk instead of gemmation froma single arm; it is the smallest heteractinic Lmclcla I have seen, thelongest arm measuring only G millim.Perrier, p. 276.11. Anthenea flavescens.Port Jackson, 0-5 fms.The Museum collection contains also specimens of this speciesfrom Fremantle, W. Australia.12. Oreaster gracilis.Pentaceros gracilis, Perrier, p. 246.Oreaster gracilis, Liitken, Vid. Med. 1871, pp. 260, 261.A selected series of five specimens, all from Port Denison (4 fms.),exhibit remarkably well the great change which occurs in thisspecies, even after a considerable size has been attained. Thesmallest, which has E, equal to 93-5 millim., has five tubercles,about 10 millim. high, one at the central end of each median rowof tubercles : in another, with R equal to 108 millim., thetubercles, though a little stronger, are no higher and are here onlyto be found on three of the angles of the disk ; this specimen, likeanother which is a little larger, has the lateral and marginal spinesvery well developed: two specimens, with P equal to 118 and140 millim, respectively, have these spines less well developed, andthe diminution is the more marked in the larger specimen ; thesmaller has one large central tubercle, and the larger has each ofthe whole set of five reduced to growths which are hardly largerthan the other spines on the disk.A specimen with six arms, one of which has been injured andhas commenced to grow again, was collected at Port Molle.