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Show 1900.] MARINE FAUNA OF CHRISTMAS ISLAND. 135 The differences between the type specimen from Torres Straits on the one band, and the specimens from Amboina, Java, and Christmas Island on the other, are constant, and render it necessary to regard the latter specimens as belonging to a well marked variety. In the type the tylostyles are longer and narrower, and the largest spirasters are smaller than in the new variety which I have named " robusta." Type. Var. robusta. Tylostyles 507 x 8 p 432 x 12 p „ head 12 p 12 p. „ neck 6 p 10 p Spirasters, smallest 8-12 p 8-12 p „ largest 36 p 48 p Distribution of S. decumbens -. Torres Straits ; of S. decumbens var. robusta : Philippines, Java, Christmas Island, Red Sea. PSEUDOSUBERITES ANDREWSI, sp. n. (Plate XII. figs. 2 a-b; Plate XIII. fig. 7.) Sponge loosely incrusting or forming free thick lamellae. Pale yellow in colour; surface smooth, and with canalicular markings beneath the dermis ; soft in consistence and easily torn. Oscules, when present, small, circular (*75 mm. in diameter), guarded by a silvery fringe or conule of tylote spicules with points centripetal. Skeleton composed of primary lines of multispicular fibres radiating to the surface and giving off at various angles a few scattered single spicules. Dermal skeleton very distinct and formed of tangentially arranged bundles of spicules joining to form a reticulum with trior quadrangular meshes. Spicules. Tylotes 350 x 6 p, slightly curved in the basal third ; head rounded, 7'5 p in diameter, slightly knobbed, at the summit or swollen laterally. Of the three specimens, one is incrusting and with oscules, the others are free and without oscules ; the former is 5-5 x 3 c.c. iu area, and '5 c.c. in thickness ; the latter are considerably thicker. The genus at present includes, as stated by Topsent, two other species, P. hyalina (Ridley & Dendy) and P. sulphureus (Bowerbank). One of the small fragments of the type specimen of P. hyalina has an oscule with the palisade of spicules arranged as in the new species, but the tylotes are much larger in the former, measuring 1100 x 25 p. HXMENIACIDON CONULOSUM (Topsent). 1897. Stylotella conulosa Topsent (18. p. 466). 1898. Hymeniacidon conulosum Lindgren (10. p. 313, pi. xvii. fig. 13; pi. xix. fig. 19). The single specimen is pyramidal, 3 c.c. in height, and with an incrusting base 3 x 1*5 c.c. The surface is partly even, and partly provided with small hispid tufts. |