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Show •562 rjR. J. S. BOWERBANK ON Nov. 2, rally to be two layers of skeleton-structure; and occasionally a portion of a third layer may be seen between them ; and this intermediate one appears to be very much less regular in its structure than either of the other two. The acutely conical spines on the fibres are not equally dispersed; on some parts they are very numerous, while on others they are much less in number. The aculei are very characteristic organs. They are of unequal length, and irregular in their mode of disposition. On some fibres a single one is projected; on others there are two on opposite sides of the fibre; and sometimes there are three or four developed in directions opposite to each other. They are rather slender, and attenuate gradually from the base to the distal extremity, which is frequently very slender and acute. The rectangulate sexradiate defensive organs are numerous ; they are of nearly equal size, and are disposed irregularly among the fibres ; but they are mostly projected into the square areas of the skeleton-rete. The canals in the skeleton-fibres are very slender, and in many of the large ones they are partially or entirely obsolete. I know of no other species for which F. aculeata might be readily mistaken except F. spinifera. The former species differs from the latter in the smallness and very much less-developed state of the canaliculation of its fibres, and in the far greater development of the minute spination of its skeleton-also in the abundance in the former species of the rectangulate sexradiate internal defences, while in the latter they appear to be totally absent. FARREA ROBUSTA. (Plate LXII. figs. 2-6.) Sponge-form cup-shaped 1 surface minutely hispid. Oscula and pores unknown. Dermal membrane thin and pellucid, abundantly spiculous ; tension-spicula long and very slender, subclavate, cylindrical, very few in number ; retentive spicula simple and contort, bihamate, small and slender, dispersed, rather numerous, and bidentate equianchorate small and few in number ; furnished also with numerous internal defensive spicula of subspinulate, attenuato-acuate forms, entirely incipiently spinous, projected at various angles from the inner surface of the membrane. Skeleton-fibres very large and strong, cylindrical, sparingly spinous or aculeated ; aculei short and slender, dispersed ; armed abundantly with rectangulate sexradiate defensive organs, radii slender, attenuated, incipiently spinous. Rete more or less quadrangular, areas frequently very little more in breadth than the diameters of the skeleton-fibres. Central canals small. Colour, in the dried state, dark amber. Hab. West Indies (Captain Hunter, B.N.I). Examined in the skeleton state. I have seen only a single specimen of this remarkable sponge. It was given, with other specimens, by the late Mr. Henry Deane to my friend Captain Charles Tyler, who kindly presented itto me for description and publication. It consists of a thin plate of siliceo-fibrous |
