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Show 302 DR. J. S. BOWERBANK O N THE SPONGIAD^E. [May 5, fig. 2, Plate XLVII., is very regularly cup-shaped, but with the addition of a small fan-shaped offset from its base ; and in a third cup-shaped one in m y possession numerous thin fan-shaped ridges are projected from the outer surface, some of which are more than half an inch in height: and I have had several fan-shaped ones of very considerable dimensions : one in m y possession is very little short of 14 inches in breadth; and many years since I gave a still larger one to the British Museum. A remarkable circumstance, which seems to prevail in the cup-shaped specimens, is that they all appear to have an orifice near the bottom of the cup, as represented in fig. 1, Plate XLVII.; but it does not always exhibit the same regularity; in the specimen represented by fig. 2, it is m u c h larger and more irregular in form. The ridged or mammillated surface-structure is the same in every form or size of the species. The dermal rete is a strong closely constructed network, so laden with particles of sand that the keratose-fibres are rarely to be distinctly seen. The oscula are situated on the m a m m a e or ridges of the exhalant or inner surface of the cup, and they are so minute as to be scarcely visible without the aid of a 2-inch lens. The primary fibres of the skeleton are mostly disposed at right angles to the outer and inner surfaces of the sponge, and each fibre has usually a single closely packed series of arenaceous particles of nearly equal size; and the distal fibres of the skeleton may be frequently seen projected beyond the outer surface, each terminated with a single molecule of sand encased in a thin coat of transparent keratode. The secondary or internal connecting fibres are mostly destitute of arenaceous matters; a few short lengths of broken sponge-spicula are occasionally found embedded in them; their general line of disposition is at right angles to the primary fibres. This species is especially interesting as exhibiting a very close alliance with Dr. Mantell's fossil species of Fentriculites radiatus, described and published in his work on the Geology of Sussex, p. 468, and figured in tables x., xi., xii., xiii., & xiv. of that work. The author instituted the genus Fentriculites for the reception of a series of fossil forms which were considered by him to be silicified Alcyonia; and in p. 168 he gives the following as its generic and specific characters :- " Generic character.-Body inversely conical, concave, capable of contraction and expansion ; original substance spongious (?) or gelatinous (?), external surface reticulated ; internal surface covered with openings or perforated papillae; base imperforated, prolonged into a stirps, and attached to other bodies. "Specific character.-Infundibuliform ; exterual integument composed of cylindrical, anastomosing fibres, radiating from the centre to the circumference; inner surface covered with perforated papillae formed by the open extremities of short transverse tubuli; stirps fixed by radical processes." The learned author accounts for the great variety of forms assumed by these animals as "partly attributable to the various forms of expansion and contraction in which the originals were introduced |