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Show 564 DR. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Nov. 2, the external surface of the sponge, but they occur in considerable numbers on the more deeply situated portions of the skeleton-fibres, whence they are projected into the areas of the skeleton-rete. They vary considerably in the amount of their development : some are comparatively short, and have their lateral radii widely spread ; and these are abundantly spinous; while others are taller and have slender and nearly smooth radii. The dimensions of one of the stouter forms was yA-j inch high, with a lateral spread of ^ ^ inch. There is no species among those whch are most nearly allied to the one in course of description with which it is likely to be confounded. The robust form of its skeleton, and the peculiarities of its membranes and its other organs strikingly distinguish the species. The abundance and variety of the forms of defensive spicula in this sponge present a striking evidence of the futility of attempting to arrange the Spongiadse by the forms of their auxiliary spicula, as it has been suggested by some imaginative naturalists. Systems founded on such bases look very learned and imposing upon paper, but when applied to the accurate discrimination of species they prove quite inadequate to their proposed purpose. In such sponges as the one under consideration, which have exceedingly thin parietes, and but comparatively small portions of soft tissues, it becomes necessary that those vital parts should be taken especial care of; and hence the profusion and variety of these minute defensive spicula to protect the vital parts, otherwise so much exposed to the numerous minute predatory creatures that exist so abundantly around them ; and hence it is that nature has in each case provided the defences most suitable to the various species, without reference to any particular type of sponges, and those only most appropriate to the purpose of the preservation of the membranous and sarcodous organs so essential to the individual's existence. In the species in course of description, we have not only the usual rectangulate sexradiate organs of defence common to so many siliceo-fibrous sponges, but we also have, in addition to them, those which are so frequently appropriated to Halichondria and many other genera differing widely in their structures from each other, to render the preservation of the delicate membranous organs of this species completely certain. In other species of siliceo-fibrous spouges of similarly delicate structure we have the floricomo-sexradiate stellate forms, as in Farrea spinulenta, which are so plentiful in several species of Geodia, a genus differing widely in its structural peculiarities from Farrea and other kindred genera. A slight doubt exists as to the true locality of this sponge, which the decease of m y late friend Mr. Henry Deane does not allow us to clear up. When Captain Tyler received the specimen from Mr. Deane, he received others of a similar description from the coast of Tripoli; but he is strongly of opinion that this species was among those that were brought up on the cable by Captain Hunter in lat. 14° 8r N., long. 77° 38' W . from 800 to 1000 fathoms depth. |