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Show 108 ZOOLOGICAL COLLECTIONS MADE DURING [Jan. 4, cases, therefore, the descriptions here given may be considered, so far as they go, as revisions of the species in question ; I believe that such revisions of many of the current species are urgently needed. Order C E R A T I N A , Carter. A P L Y S I N A ( ? ) R E G U L A R I S , sp. n. (Plate X. fig. 1.) Surface even, set with the slightly projecting ends of the primary skeleton-fibres at intervals of about "5 millim. Vents inconspicuous. Skeleton regular, of primary fibres at right angles to surface, average greatest diameter "057 millim. ; and of secondary fibres, parallel to the surface at regular intervals between the primaries, average greatest diameter about half that of the primaries. Primary fibre pale amber-colour, composed of a multilaminar horny wall with a thick innermost lamina, enclosing a faintly granular axis closely resembling the wall in nature of substance ; axis about one third the diameter of the fibre. Secondary fibre paler, generally fibrillated to its centre. Examined. In spirit and by mounting in balsam. External Characters. Form incrusting. Consists of a sheet of substance about 2 millims. thick, with a level surface, spreading irregularly over about one square English inch of an immense flexible worm-tube. Texture soft, very elastic. Colour (in spirit) pale grey. The surface appears glossy, and is set with a number of minute projecting points, which occur with some regularity at about g-millim. intervals over it. Vents. None apparent. Pores scattered between surface-points, •04 to "1 millim. in diameter. Main Skeleton. Composed of a set of primary fibres running outwards at right angles to surface, and projecting by attenuated points to a distance of from "14 to "32 millim. from the surface (they are distant from each other at the surface "35 to "7 millim.), of a secondary set, connecting these, approximately at right angles to them, distant from each other by "18 to '36 millim., and of a tertiary set, running parallel to the primary fibres and connecting the median portions of the secondary fibres. This tertiary set is not always so fully developed as to extend from the base to the surface of the Sponge; but it is generally represented by a fibre or two in the interval between each two primary fibres ; it may possibly prove to be merely the voung stage of the primary fibres, from which it differs in its diameter and structure, being about half as broad as an average primary fibre, and having but a thin uni- or bilaminar outer wall, and pale yellow colour, also apparently in not terminating on the surface by a point : it may give rise to a primary fibre. Hab. Sandy Point, 7-10 fathoms, on worm-tube. Obs. This is probably quite a young specimen; its habits and size, as compared with those of the other members of the genus Aplysina, seem to show this. The extremely slight difference in appearance between the horny wall of the primary fibre and its granular axis distinguishes it from most, if not all, other Aplysince. |