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Show 1875.] SILICEO-FIBROUS S P O N G E S . 559 it to Farrea until further information on the subject enables us to assign it more correctly to its proper place among the siliceo-fibrous sponges. The primary skeleton-fibres are large and cylindrical, but of unequal diameter, and mostly have the appearance of transparent longitudinal striation from their strongly marked lines of growth, and they are more or less minutely spinous; their course is irregular, not running in straight lines, but in meandering ones, branching at intervals and again anastomosing with each other. Their large conical defensive organs are not all systematically projected outwards at about right angles to the dermal surface; some are so disposed, while others have a lateral direction, or are projected at various intermediate angles. The central system of canals in the primary fibres is subject to considerable irregularity. Sometimes they are regularly confluent; at others they are produced in opposite directions, and their distal ends pass each other, and each has a caecoid termination. It is not an unusual circumstance to see a short sexradiate arrangement of canals within one of the large fibres, as if the process of the production of new branches was first, the development of the canals within the parent fibre, and then the projection of the young offshoots in accordance with the nascent canals. In some cases there is not the slightest indication on the surface of the large fibre of the coming offshoot, while in others there is a very slight elevation on its surface immediately above the nascent canal; or the young shoot, in the form of an acutely conical projection, is unmistakably present with the continuation of the canal iu its centre to its apex, where it usually appears to be open in the early stage of its development, with extremely delicate margins; but in a more advanced stage of its growth tbe apex becomes solid. These projections of young branches are readily to be distinguished from the conical external defences by their canals, while the defensive organs appear to be perfectly solid. The inner external surface has the same characters as the outer one, but the dermal skeleton-fibres seem to be rather more slender. The intervening skeleton is more regular in its construction than the external layers. The reticulation is more regularly quadrate and the areas smaller. The fibres are also smaller and more profusely spinous; and the central canals are more continuous and confluent than those of the fibres of the external surface, and in some parts they are densely coated with dark-coloured opaque sarcode. I could not detect the slightest traces of any detached spicula amidst the structures. This interesting specimen is in the cabinet of m y friend Mr. IT. Deane, who, I believe, received it with other specimens from Captain Hunter, R.N. Since the above description was written, I have received another specimen of this species from my friend Mr. Deane. It is about four lines square, and is closely attached by one of its broad surfaces to the side of a small fragment of a Vermetus, and does not exhibit PROC. ZOOL. Soc-1875, No. XXXVI. 36 |