OCR Text |
Show 124 ZOOLOGICAL COLLECTIONS MADE DURING [Jan. 4, TEDANIA TENUICAPITATA, sp. n. (Plate XI. fig. I.) Massive, almost white. Surface bearing scattered shallow pits from about '1/ to 1 millim. in diameter. Texture very soft and fragile. Vents small, scattered. Pores scattered. Main skeleton a very loose network of spicules, with triangular to polygonal meshes, extending from base to surface, crossed at nodes by spiculo-fibres lying parallel to surface ; sides of meshes formed by groups of 2 to 5 acuate spicules (sometimes of cylindrical spicules in whole or in part), scarcely touching. Dermal skeleton composed of sheaves of 20 or more cylindrical spicules, closely aggregated at one end, and radiating outwards with the other over the surface. Parenchyma very pale yellow to colourless, finely granular. Skeleton-spicules of two kinds, viz.:- (i) smooth curved acuate, tapering to a sharp point from a distance of about 6 diameters from the point, size "38 by "01267 millim.; and (ii) cylindrical, double-headed, smooth, heads about one third as broad again as shaft, and oval, drawn out to a point, occurring in main skeleton, and alone forming dermal skeleton, size "2787 by "006334 millim. Flesh-spicules acerate, tapering from centre to very fine points, roughened almost imperceptibly on surface, one end slightly the stouter, scattered, size '316 by '0021114 millim. Examined. In spirit, and by mounting in balsam. External Characters. The single specimen forms a small subpyra-midal mass, whose four uninjured faces form rounded angles of about 120° with one another. It appears to have been broken from a mass sessile by a broad triangular base. Among the numerous small pits of the surface, in which many of the pores are collected, and between which the Sponge forms insignificant ridges, are distributed the five vents which are still left. Three of these are close to the apex; they open on the surface level, and penetrate straight into the Sponge to a depth of 3 to 8 millims., where they suddenly terminate; they are oval, and 1*5 to 2 millims. in diameter. The pores lie on the ridges and in the small surface-pits. The main skeleton is very vague, the spicules of the fibre being hardly in contact; it consists generally of the stout acuates; but sometimes groups of 6 to 10 cylindricals take their places, or they are mixed with a few of these ; a horizontal network of stout acuates occurs throughout, but is especially developed just below the dermis. The dermal-skeleton bundles appear to radiate from certain centres with more or less regularity. The parenchyma is very transparent, and is sufficiently well preserved to show, in Canada balsam, numerous round nuclei, of about •0095 millim. diameter, transparent, and nucleolated. The cylindrical spicule differs from that of all hitherto recognized species of the genus in being terminally pointed ; the heads are verv slightly marked and suboval in outline, and are not microspined as in the Mediterranean and Malacca species already known. The fine acerate has, as in other species, one end stouter than the other, though very slightly so: the roughening of the surface is often imperceptible ; it takes the form, as far as can be made out, of sub-spiral scratches. |