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Show 1873.] DR. J. S. BOWERBANK ON THE SPONGIADcE. 327 regularity does not extend beyond the length of the shafts of the connecting-spicuia ; all beneath that point to the centre of the sponge is entirely devoid of regularity. The intermarginal spaces and the interstitial membranes within them are crowded with the stellate retentive spicula ; but below the terminations of the retentive spicula they were comparatively few in number, and in the inner and central parts of the sponge they are rarely, if ever, to be found. The retentive stellate spicula are of two descriptions. The attenuato-stellate ones are small and nearly uniform in size, a few large ones occasionally appearing among them. The cylindro-stellate ones are very minute, not exceeding one third or one fourth the diameter of the average-sized attenuato-stellate ones. I did not succeed in finding the slender porrecto-ternate or recurvo-ternate spicula in situ; but a few fragments of each were found among the spicula obtained by the aid of nitric acid. By the same means also I detected the presence in the sponge of a few deltoid spicula. PACHYMATISMA CONTORTA, Bowerbank. (Plate XXXI.) Sponge branching ; branches irregular, short, stout, anastomosing; surface undulating. Oscula simple, dispersed, small. Pores inconspicuous. Skeleton-spicula acerate, large and long, and occasionally acuate, large and long. Connecting-spicuia attenuato-patento-ternate, rare and verv variable in size. Interstitial membranes- tension-spicula acerate, short and stout; retentive spicula attenuato-stellate, comparatively large, and attenuato-sphero-stellate, minute ; radii more or less acutely conical. Ovaria obtusely oval, slightly depressed, component cuneiform spicula small and slender. Colour, in the dried state, light brown. Hab. Fiji Islands (Sir Everard Home). See Catalogue of Porifera in the Museum of the Royal College of Surgeons, part i. I860, p. 126, B. 166. The short branches of this sponge vary in diameter from 3 to 9 lines, and in the greater part of the sponge are so much anastomosed as to almost form an irregular mass. The surface is somewhat uneven and undulating; and in some of the most protected parts there are a few spicula that project from between the ovaria ; but the specimen has so many fragments of parasitical sponges attached to it as to render the slight proofs of its hispid character doubtful. The oscula are few in number, and the largest was scarcely a line in diameter. I could not determine the characters of the pores, in consequence of the destruction of the dermal membrane by weathering or washing. The dermal crust of the sponge is hard and very compact, and in some parts attains a thickness of nearly a line. The radiating structure immediately beneath the dermal crust, so striking and characteristic in the greater number of the species of this genus, is in this species almost obsolete; and the irregular central portion of the interstitial tissues extends in many places quite to the inner surface of the dermal crust; while in other parts the |