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

;;;450 COLLECTIONS FROM MELANESIA.79. Rhaphidophlus arbor escens, (Plate XL. fig. LPlate XLII. tigs. «, n .)Sponge stipitate, mucli branched, bush-like ; branches angularrather than cylindrical ; surface nodular, connected by frequenthorizontal trabeculaj at right angles to the erect branches. Theaverage diameter of the stem and its branches is 4-5 millim. Thecortical incrustation of spicules consists of a layer about '5 millim.thick, the outer part of which consists of loose fascicles of thesmooth spinulate spicule, with the pointed ends placed outermostthe spicules are closely approximated to each other below thesurface, between the intermarginal canals, but their distal endsdiverge and spread out somewhat at the surface, and betweenthem appear to be placed the pores ; the intermarginal canals,as stated, lie between the bases of these fascicles. The deeperpart of this layer consists of Halichondrioid spiculo-fibre, about 6-8spicules broad, with small roundish or polygonal meshes, which seemto have enclosed small canals (probably the afferent canals leadingfrom the intermarginal cavities to the ciliated chambers). Nohorny matter is to be seen in this part of the skeleton, the extremefragility of which forbids the idea that any such occurs here [onthe contrary, the compressibility and readiness with which thespicules and fibres must be able to move upon each other in life,owing to the manner of their aggregation, point to a probable greatpower of contractility and expansion in the dermal membrane, withimportant consequences to the pores, intermarginal cavities, andinhalent canals which it contains ; and I should anticipate that goodspirit-specimens would show the strong development here of musclecells,such as has been shown by Prof. Sollas in Tetilla (Ann. &Mag. N. H. 1882, ix. p. 155)]. The fibres of the skeleton are irregular; their course is winding, and the distinction between primaryand secondary fibres not clear, except at the surface ; here the endsof the primary fibres, which stand out for some distance bej'ond thegeneral reticulum and support the dermal crust, are absolutely concealedby the enormous abundance of points of the spined spiculeswhich project :— from them.Spicules (1) Slightly spinulate, smooth acuate, -34 by -0063(2) Spined acuate, slightly constricted basally, -08 by -0044(3) Delicate equianchorate, palms proximally square, -012 millim.long.Hah. Friday Island, Torres Straits.The specimen, which is dry, measures 125 millim. (5 inches) inheight and 60 miUim. (2^ inches) in maximum diameter.Vosmaer's ClatJiria ulmns (Notes Hoy. Mus. Netherl. ii. p. 151)resembles this species, but is stated to have a bihamate fleshspicule,and no dermal crust is described. The species differs fromR. cratitiiis, Esper, in the well-branched habit and in minor points in