OCR Text |
Show I 868.J DR- J- E. GRAY ON THEONELLA. 565 the cysts covering the ends of the mass like the rest of the body. The cysts are hard, cartilaginous, rather convex externally, with two concavities having an opening at the base of each. The apertures are slightly raised round the edge; and the centre is closed with four short valves, leaving a stellate 4-rayed aperture. The outer surface of the cyst is covered with a thick hard skin, strengthened externally with imbedded particles of sand, which are more abundant and clustered in certain parts, especially in those sunk below the general level of the surface. The animal is full of sand, in rhombs and crystals. 6. Note on Theonella, a N e w Genus of Coralloid Sponges from Formosa. By Dr. J. E . G R A Y , F.R.S., V.P.Z.S., &c. Mr. Swinhoe sent to the British Museum in 1867, along with some other marine productions, a small specimen of coralloid sponge. The outline of the cup is irregular, and the base of the cavity imperfect, which induced me to consider that the species was imperfectly developed. Though I promised to describe it, I have waited in hopes that I might obtain a more perfect specimen; but Mr. Swinhoe has now left Formosa, and informs me that he is not likely to obtain any other specimen. The sponge in some external characters is like the genus Macandrewia, but it differs from that sponge in not having any stellate spicules, or at least Mr. Cooke, who has kindly examined the sponge for me, did not discover any. It is, I believe, the only sponge of the family in which they have not been discovered. THEONELLA. Sponge cup-shaped, thick, covered with a smooth rather coriaceous external coat; internally formed of netted spicules, arranged so as to leave an hexangular mass ; the spicules subcylindrical, united at the inosculation of the network by a siliceous callosity; the body of the spicules generally smooth, but sometimes slightly spiculate on the surface, with numerous very slender fusiform spicules of very different sizes mixed in the sarcode. The parietes of the cup are pierced with many cylindrical tubes opening on the edge of the cup ; but there is no appearance of any spines or oscules on the edge or surface of the dry specimen. The spicules form a coral-like network, very like Macandrewia. Their intersections are rough and tubercular, like the knots of a net, but more rugose; the spicules themselves are generally smooth ; but some of them are more or less spinulose, with short acute tubercles. Tbe fusiform spicules in the sarcode are abundant, very slender, slightly tapering and acute at each end; they vary greatly in length, but are always slender and smooth ; they are generally straight, but some few are curved like a nearly expanded bow. PROC. ZOOL. Soc-1868, No. XXXVII. |