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Show •524 DR. A. GUNTHER ON A ZOOLOGICAL [June 23, IX. PORIFERA. By A R T H U R DENDY. Only a single Sponge was brought home by H.M.S. ' Flying-Fish,' but this specimen is one of considerable interest. It belongs to a new species of Schmidt's genus Pachychalina l. It is only very rarely that specimens of Chalinine Sponges come to hand in a sufficiently well-preserved condition to allow of an investigation into the structure of the soft tissues. Such investigation is likely to prove of much importance in determining the true relations of this large and difficult group of Sponges. Hence, as no account has ever yet been given of the minute anatomy of any species of Pachychalina, and, as indeed, only one or two Chalinine Sponges have been anatomically described at all, I have thought it desirable to give some description of the minute anatomy of the present species- a proceeding rendered practicable by the excellent state of preservation of the specimen. PACHYCHALINA SPINOSISSIMA, n. sp. (Plate XLIV.) The single specimen in the Collection (Plate XLIV. fig. 1) consists of a long, unbranched, irregularly cj lindrical, repent stem, naturally terminating at each end. The specimen has evidently been attached by various parts of the lower surface to the sea-bottom. It is covered all over with very large, stout, sharp-pointed, and often branching spines (whence the specific name), and bears along the upper surface a row of large oscula. Total length of specimen about 350 millim. (=14 inches); average diameter, exclusive of spines, 12 millim.; average length of spines, 10 millim. Colour in spirit brownish yellow. Texture compressible, elastic, tough, internally cavernous. Surface subglabrous over and between the spines. Dermal membrane (ectosome) very thin, delicate, and transparent, reduced to a mere network by the very numerous pores (Plate XLIV. fig. 2). Pores very numerous rounded openings, thickly scattered through the dermal membrane, averaging about 0'05 millim. in diameter (Plate XLIV. fig. 2). Oscula circular, pit-like openings, having their margins flush with the general surface ; averaging in diameter about 3 millim. ; arranged in a single series along the upper surface of the sponge (Plate XLIV. fig. 1). Skeleton.-(a) Main : a coarse, irregular, wide-meshed reticulation of stout spiculo-fibre, in which there is a strongly developed but rather irregular system of fibres running more or less longitudinally hi the direction of the long axis of the sponge, The fibres themselves are, as in otber species of the genus, stout and polyspiculous; each consists of a stout spicular axis, composed of very numerous, closely packed spicules lying side by side parallel with one another, and a large proportion of spongin, which unites the spicules together, and, generally at any rate, also forms a distinct sheath around the 1 Vide Ridley and Dendy, Eeport on the Monaxonida dredged by H.M.S. ' Challenger,' p. 19, for diagnosis and discussion of the genus. |