OCR Text |
Show 292 DR. J. S. BOWERBANK ON THE SPONGIADcE. [Apr. 6, largest of them measured TY^TRF ^nc^ m diameter. In these smaller ones there also exists another peculiarity; and that is that the terminal teeth are given off at nearly right angles to the axis of the shaft. These peculiarities of the tension and retentive spicula of the dermal membrane, combined with the eccentric and singular form of the sponge, afford excellent specific characters to discriminate this from any other nearly allied species. HALICHONDRIA VARIA, Bowerbank. Sponge massive, sessile, variable in form. Surface smooth or rough and rugged. Oscula simple, dispersed. Pores inconspicuous. Dermal membrane spiculous, reticulated ; rete unispiculous ; spicula acerate, stout, same size and form as those of the skeleton ; retentive spicula bihamate, simple and contort, minute and slender, very numerous. Skeleton-rete compact, uni- or bispiculous ; areas unsymmetrical ; spicula acerate, short and stout. Interstitial membranes- retentive spicula bihamate, simple and contort, slender and minute, numerous. Colour, in the dried state, dull ochreous yellow. Hab. Straits of Malacca (Commodore Parish). Examined in the dried state. The external characters of this sponge are exceedingly variable. Sometimes it appears as a rough and irregular mass, full of small ridges and prominences; at other times it assumes the form of short cylindrical branches, with a surface comparatively smooth, and with the oscula well developed ar.d evenly distributed. Notwithstanding these striking variations in form, the structural characters are exactly the same in every specimen. The most striking specific characters are exhibited in the dermal membrane, the unispiculous rete of which is a very beautiful object when mounted in Canada balsam. The rete is seldom more than one spiculum in width; and the areas vary to a very considerable extent in form; and the membranes filling the areas are in many cases crowded with the minute slender bihamate retentive spicula. These spicula are very small and slender, and require a power of about 300 linear to define them in a satisfactory manner. Their length does not exceed twice the diameter of a skeleton-spiculum. The skeleton-rete is compact and strongly constructed, with but slight approaches to symmetry. The areas are very variable in form, and each side rarely ever exceeds one spiculum in length. The short stout acerate spicula of which it is formed are the same in length and form as those of the dermal rete. Within the mass of the sponge there are frequently to be seen interstitial cavities of comparatively considerable size; and in the lining membranes of these the minute bihamate retentive spicula abound to quite as great an extent as in the dermal membrane. I received several small specimens of this sponge from my friend Commodore Parish who obtained them from the Straits of Malacca. |