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

390 COLLECTIONS FROM MELANESIA.Main skeleton forming rectangular meshes ;primary fibres strong,running at right angles to surface, exhibiting horny margins (whichmay form as much as one third of total thickness of fibre), about•2y to '35 millim. apart, "1 to -18 millim, thick. Secondary fibresvertical to primaries, at about the same intervals, either withoutforeign bodies or with only about half to two thirds of the thicknessoccupied by them ; in the former case -035 to "043 millim. thick, iathe latter •053 to '1 millim. thick. Longitudinal fibres {^primanj ofMarshall) of same structure as primaries, but less horny, '18 to '28millim, apart, -14 to -21 millim. thick, running upwards and spreadicgout somewhat from each other. Dermal skeleton composed oflong compound fibres, the primaries running parallel to each otherand to the long axis of the sponge, '35 to -43 millim. apart ; thesecondaries extended between them at considerable intervals ;primaries-14 to -28 millim. broad, secondaries -1 to '14 millim., thehorny matter of the former usually, of the latter often, obscured bythe foreign bodies, which often project much from the fibre. Hornysubstance amber -yellow. Sarcode amber-yellow, transparent.Foreign bodies of fibres small, chiefiy sand.Ilab. North-east coast of Australia.The single specimen is 105 millim. (41 inches) high by 65 millim.greatest width. In its even compact surface it differs from all otherDysidece except D. favosa, Marshal], with which it also agrees inthe large development of the tubular form which it exhibits. Thestrongly horny character of the secondary fibre, however, distinguishesit from this (as from most, if not all other) species, andallies it to Hircinia. These striking characters, and the good preservationof the specimen, seem to warrant its description.18. Psammopemma densum, Marshall, var. subfibrosa.(Plate XLI. fig. 7t.)Psammopemma densum, 3Iarshall, Zeitsch, tviss, Zool. xxxv. p. 113.Agreeing closely in size and external characters with Marshall'saccount of this strange form is a specimen in spirit in the presentcollection. It has the size and almost the shape of a horse-bean,and is of a grey colour. The dermal membrane contains numerousforeign bodies, but is in parts transparent, though fibrillatcd. Owingto an inferior amount of contained sand, a distinct network of whollysandy fibres is to be made out, which Marshall did not find in his specimens; the meshes are round, about -3 millim. in diameter, in thenatural state almost filled up with sarcode containing foreign bodies.Sarcode very pale brown, subtransparcut. The radiating tubes indicatedin Mai'shall's figure (0) appear to me possibly to representspaces between primary fibres; but those fibres in the present specimenare not straight, but bend right and left to meet the short secondarylines ;thus a vertical section of the sponge exhibits a somewhathoneycomb-like appearance. No trace of horny matter was observed.Hab. Thursday Island, Torres Straits, 3-4 fms.Distrihittion. Tasmania (Marshall).