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Show 28 DR. J. S. BOWERBANK ON CEYLONESE SPONGES. [Jail. 7, Where the true fibre prevails, and the increment of the skeleton is progressing, a single thread may be seen projected from the outer surface of a grain of sand, to some distance, without having met with a grain to which it could attach itself, and at its distal extremity there will be seen a single large or small molecule of sand elevated, as it were, on a pedestal, or an irregular cup-shaped membrane which has only partially enveloped a particle and then lost it; or a column of large and small grains will be seen projected from the mass, the distal grain of which always exhibits more or less extensions of keratose tissue in search of additional grains of saud to be incorporated in the fibrous skeleton of the sponge. The dermal membrane is thin and pellucid ; it is covered with a single stratum of grains of sand and a few foraminated shells ; in the interstices of these grains a few open pores were visible. The oscula are variable in size ; ten or twelve were dispersed over the surface of the sponge; the largest rather exceeded a line in diameter. ISODICTYA DONNANI, Bowerbank. (Plate VI.) Sponge cup-shaped, parietes thick and strong; margin strongly undulated, distal edge finely plicated, surface externally and internally even, minutely hispid. Oscula and pores inconspicuous. Dermal membrane abundantly spiculous; spicules the same as those of the skeleton, and very small and slender acuate ones, dispersed. Skeleton- primary lines multispiculous, strongly developed, rather irregular ; secondary lines very irregular, varying from multispiculous to unispiculous, very numerous; spicula acuate, short and stout. Interstitial membranes abundantly spiculous ; tension-spicula acuate, small and slender, dispersed, rather numerous. Sarcode dark amber-colour. Colour, alive, bright orange ; dark purple in the dried state. Hab. Pearl-banks, Ceylon (Mr. Holdsworth). Examined in the dried state. I have named this species after Capt. Donnan, the present Superintendent of the Pearl-banks. I received a single specimen of this interesting sponge from Mr. Holdsworth for examination. The parietes of the cup are remarkably firm and thick; and at about half its height from the distal end of the short pedicle the undulation of the marginal portion of the cup commences, and increases to such an extent as to occupy at least two thirds of its entire diameter. The extreme edge of the cup is thick and rounded, and is plicated in such a manner as to closely resemble the distal end of a lady's fan when in a closed condition. The short basal column does not exceed half an inch in height in its present condition. It has every appearance of having been broken from its natural attachment while in a living state. The surface of the outer and inner portions of the cup are even, but not smooth to the touch, from the projection of the terminations of the primary lines of the skeleton. The hispidation is visible only |