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Show 1867.] DR. J. E. G R A Y O N SPONGES. 547 Fam. XENOSPONGIAD^E. XENOSPONGIA, Gray, P. Z. S. 1858, p. 230. XENOSPONGIA PATELLIFORMIS, Gray, ib. Rad. pl. XII. B.M. Hab. Torres Straits. The genus Halicnemia (Bowerb. B. S. i. p. 184, t. 32. f. 363, 364, ii. t. 96) has the same form as the former. It has a small pebble imbedded in the centre ; but, from the description and the figures, I have little doubt that it is distinct from the above, though it may belong to the same family. It contains many imbedded short pin-shaped spicules, and some oblong tubercular bodies like ovisacs (see f. 364). But there are many differences in detail that show it must be a very distinct genus; for example, the oscules are numerous on the lower, concave surface, the upper surface is covered with extraneous matter, and the lower one clear of such impurities. Section II. CHLAMYDOSPORJE. Reproduction chiefly by ova contained in defined ova-cells or "ovaria," strengthened with siliceous spicules, sometimes at length becoming solid spheres formed of siliceous spicules radiating from a central point. Order VI. SPHCEROSPONGIA. The ovisac cells composed of closely packed fusiform spicules diverging from the centre, which, when the ova are emitted, extend internally and fill up the cavity, forming the ova-cells into nearly solid balls, formed of spicules diverging from the centre to the circumference, which are congregated together, and form a hard external coat to the sponge. Fam. 1. GEODIADCE. Sponge massive, fleshy, cellular within; pores with a regular constrictive valve. Ovisacs subgiobose or oblong, with a thick coat formed of spicules in lines, radiating from the axis to the circumference, and at length becoming solid, congregated on the outer surface, or scattered in the flesh. Spicules elongate; the larger ones with two or three expanded or recurved branches on the outer ends ; smaller ones simple, often extending beyond the surface. I. The ovisacs forming a thick external covering to the sponge. 1. PACHYMATISMA, Bowerb. B. S. i. p. 171, ii. p. 51. Sponge massive, irregular. Ovisacs forming a continuous external covering to the sponge. Spicules uniform, very slender ; outer ends with two or three diverging branches. PACHYMATISMA JOHNSTONIA, Bowerb. ib. ii. pp. 51, 172, f. 15, 16, 17, 20, 21, 45, 46, 93, 158, 159, 330, 331, 332, 353. Halichondria johnstonii, Bowerb. B.M. |