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

592 COLLECTIONS FROM THE WESTERN INDIAN OCEAK.fibres, meeting the surface at various angles, and projecting slightlyaboveit, and of a system of crossing fibres connecting the two andforming approximately rectangular meshes, their direction beingroughly vertical to one or other of the above systems. The meshis very variable in diameter, viz. from -07 to -24 millim., the formerchiefly at the surface. The diameter of the main fibre is 'OSS-'O?millim., not including the ditelous network of fibres of small diameterwhich often surrounds the bases of the large primary fibres.Colour of fibre pale amber-yellow ; no foreign bodies imbedded inany part of the skeleton ; the fibre is homogeneous in appearance,with the occasional exception of a faint granular axial line. Sizeof sponge, 80-95 millim. (3-3| inches) in greatest diameter.Hah. African Island, Amirante group (gathered on beach).Distribution. "Indian Ocean?" (Pallas); Indian Ocean (Za???rtrfZ;);Mauritius (Hyatt).Hippospongia sinuosa, Pallas, var. decidua, Hi/ait.The other variety of the species is very distinct in its externalappearance, but on examination this is found to be due merely tomodifications of the same structural arrangements as those of var.mawitiana. The surface is entirely broken up into small isolatedtufts, or short meandrine ridges, llattened externally, about 1-2miUim. in diameter (the ridges of mauritiana being 3 or 4 millim.across), rising from a considerable depth, viz. 7-15 millim., andcommencing below by very narrow bases, and not expanding untilclose to the surface. By the juxtaposition of these tall walls andtufts, a number of freely intercommunicating, very narrow (2 to 2-5millim. wide) and deep channels are formed, very different in appearancefrom the subcjdindrical and semi-tubular canals which representthem in var. mauritiana. The outward form of the spongeis essentially similar to that of the other variety, but the specimensare much larger ; the largest, an example of incrusting growthabout 30 millim. in average vertical thickness, measures 275 millim.(11 inches) in greatest diameter; some smaller specimens attainabout twice the thickness. As in var. mauritiana, the tubular characterof the channels of the skeleton is much more strongly markedon the lower surface, where (as observed by Hyatt) connectinglaminae of horny fibre frequently bridge over the spaces between thesummits of the tufts and ridges. The colour of well-preservedskeletons is a rather pale aml}er-yellow ; those which have sufferedmuch washing on the beach are almost white.The general arrangement of the skeleton is similar to that of theother variety ; but the following important differences are to benoted :—(1) It is the primary and not the secondary fibres whichare the most distinct elements of the deep skeleton ; they foi mcontinuous, almost straight lines, •4--5 millim. apart, and areplaced vertically to the surface. The primary fibres of theouter surface form a decided pile of short projecting points, beingmuch more numerous than in var. mauritiana. (2) Owing to the