OCR Text |
Show 1875.] DR. J. S. BOWERBANK ON THE SPONGIADcE. 293 HALICHONDRIA PURPUREA, Bowerbank. Sponge massive, sessile. Surface very rough and rugged. Oscula simple, dispersed. Pores inconspicuous. Dermal membrane spiculous ; tension-spicula fusiformi-acuate, rather slender, longer than those of the skeleton, very numerous; retentive spicula bidentate equianchorate, very minute, equable in size, numerous. Skeleton-rete very coarse and open; fibre multispiculous, very stout and compact ; spicula fusiform acuate, short and stout. Interstitial membranes spiculous ; spicula same as those of the dermis, dispersed, numerous. Sarcode dark purple. Colour, in the dried state, dark purple. Hab. Straits of Malacca (Commodore Parish). Examined in the dried state. Among the sponges from the Straits of Malacca which I received from my friend Commodore Parish, there was a specimen of a Sertularia, on which there were four species of parasitical sponges located, and among them the one in course of description. It is a small mass about half an inch wide at the base, gradually decreasing in size, and terminating acutely at the height of ly inch, of a deep-purple colour. The surface is remarkably rugged, full of deep pits and sharp elevations. The dermal membrane is very characteristic of the species; it abounds in spicula ; the tension ones are frequently nearly twice the length of the skeleton ones, while they are very little more than half their diameter. They are very numerous, in some parts forming flat wide fasciculi, and in others they are scattered indiscriminately over the surface of the membrane. The retentive bidentate equianchorate ones are also very characteristic; they are slender and delicate in form, very equable in size, and very minute; they do not exceed y-3^3 inch in lengtb, or twice the diameter of a fully developed skeleton-spiculum, which measured ^Af^ inch in diameter. Nearly the whole of these spicula, seen in situ, were firmly attached to the surface of the membrane by the middle of the convex back of the shaft. They were very numerous on some parts of both the dermal and interstitial membranes. Occasionally a few also of the short stout skeleton-spicula were mingled with the tension-spicula of both the dermal and interstitial membranes. The skeleton-structure is remarkably coarse and strong, the fibre containing a far greater number of spicula than is usual in skeletons of the genus Halichondria, and the areas are wide and irregular in their form. These peculiarities of structure seem to indicate that this species attains a much greater size than the specimen under description. The whole of the internal sarcode, as well as the external portions of the sponge, are of a dark purple colour. ISODICTYA RUDIS, Bowerbank. Sponge massive, sessile. Surface rugged and very uneven. Oscula simple, dispersed, numerous. Pores inconspicuous. Dermal membrane abundantly spiculous ; tension-spicula acerate, long and slender, numerous, dispersed. Skeleton-texture coarse and irregular ; pri- |