OCR Text |
Show 1873.] DR. J. S. BOWERBANK ON THE SPONGIADCE. 329 have had a small collection of oscula at the bottom of it originally; but the dilapidated condition of the specimen allows of nothing more definite than a conjecture on the subject. The porous areas were not evenly dispersed over the surface; and two or three small groups of them only were apparent, marked by the usual pitted appearance that indicated the presence beneath of the intermarginal cavities. On this portion of the specimen the dermal membrane was in a tolerably perfect condition, and contained an abundance of minute sphero-stellate spicula, like those of the interstitial membranes, in which they were also rather abundant. These minute organs are very characteristic of this species. The spherical centre of a fully developed one measured -^TVO" inch diameter, and the spiculum between the extreme apices y ^ W inch. They are very similar in form to the sphero-stellate spicula of Tethea lyncurium, but are very much more minute, and the number of the radii is much greater ; but they resemble those of T. lyncurium very much in their conical form. I have not before found this form of spiculum in the sarcode of a Geodia. The diameter of a fully developed ovarium was g-|^- inch. The cuneiform spicula of which they are composed are large in proportion to the size of the ovarium, and the the distal extremities are much angulated. GEODIA PAUPERA, Bowerbank. (Plate XXXI.) Sponge massive, coating ; surface even, smooth. Oscula simple ; congregated in depressed areas. Pores congregated. Dermal membrane thin, pellucid. Connecting-spicuia attenuato-expando-ternate, variable in size and proportions, rather few in number. Skeleton abundantly spiculous ; spicula fusiformi-acerate, comparatively small and short. Interstitial membranes-tension-spicula subfusiformi-acerate, small and slender ; retentive spicula cylindro-stellate, variable in size and structure, and very minute cylindro-stellate; radii short and stout. Ovaria globose ; cuneiform spicula of adult specimens comparatively large, distal ends prominently angulated. Colour, in the dried state, cream-white. Hab. Unknown. Examined in the dried state. I am indebted to Mr. Jeremiah Slade for my knowledge of this species. It was purchased at a public sale of specimens of natural history from various localities. It is based on an irregular mass of coral, an Astreea, about 4 inches in diameter, on which has grown a specimen of Gorgonia flabellum and a compound tunicated mollusk ; the latter has very nearly covered the Geodia, which is about 2 inches in length, and rather exceeding an inch in breadth. The specimen has suffered much by maceration, and nearly the whole of the dermal membrane has been destroyed; the little that remained was thin and translucent, but in such a condition as to afford no other specific characters. In sections made at right angles to the dermal surface, large intermarginal cavities were apparent, passing through the dermal crust from its outer to its inner surface, which is covered |