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

420 COLLECTIONS FROM MELANESIA.matic position, which Carter (I.e.) is inclined to regard as amongthe RenieridiB, I notice that Rhizochalina oleracea, at any rate, hasa true Chalinid fibre ; 1)ut Bowerbank's and Carter's species neverapproach this condition more closely than by producing a fewscattered compact fibres, wholly composed of spicules, like those ofsome Pachychdlince : but the greater part of the organization isReuierid, and it appears to approach 8chmidtia, Balsamo-Crevelli.On the other hand, Oceanapia, which seems to be nearly allied, hasthe bihamate spicule. Taking this fact in conjunction with thehorny fibre of Rh. oleracea, it seems to me best to place the twogenera in the Desmacidiuidae.54. Rhizochalina fistulosa, Bowerhank\ var, infradensata, nov.? Alcyonium putridosum, Lamarck, Mem. Mus. Hist. Nat. i. p. 168.DesDiacidon fistulosa, Bowerbank, P. Z. S. 1873, p. 19, pi. iv. figs. 7, 8.Two more or less imperfect specimens in spirit, the largest about25 millim. (1 inch) across the body, and some detached dry tubes.An arrangement here found, which 1 have not seen described inthis species, is that of a dense layer of the skeleton-spicules, packedside by side, at right angles to and about "25 to "8 millira. below thesurface of the sponge—below, that is to say, the superficial Isodictyal,or rather Halichondrioid (in Bowerbank's sense) network containingthe subcortical crypts and other cavities. This layer recalls the verticallayer of small subspinulates of Binalda uberrima, Schmidt, onlythat it is not, as there, placed at the surface. It is represented inthe type specimen of the species by a layer in which the sjjicules areset obliquely to the surface at various angles. As both the presentspecimens present this peculiarity, I think it well to establish forthem a distinct variety.Oue of the specimens exhibits the small crateriform eminencesfigured on the outside of Bowerbank's specimen, but the other doesnot ; hence they probably have no systematic, and but little physiologicalimportance. The spicules agree closely in proportions withthose of the type.Arafura Sea,Arafura Sea,Type specimen. Spec. no. 1. Spec. no. li.Acerate spicule. . -27 by -01 1 to -0127 -20 by -Oil -25 by -012 mm.Hah. Arafura Sea, N,W. coast of Australia, 32-36 fms.-; bottommud, sand, and shells.Distrihiition. Fremantle, W. Australia (Botuerbaiik) (the typicalform).The dermal membrane of one of the specimens contains a largenumber of smooth acerate spicules of about half the length andbreadth of the proper spicules ; they do not occur below the membrane,nor, apparently, in the other specimen. A similar circumstanceoccurs in R. siac/aporensis described below ; in that case anumber of short blunt cylindrical spicules occur of the normal, oralmost the normal thickness, but only one half to two thirds thelength of the adult form.