Proceedings of the Scientific Meetings of the Zoological Society of London 1875

Page 356

296 DR. J. S. BOWERBANK ON THE SPONGIADcE. [Apr. 6, than those of the dermal membrane; but the whole of the spicula are rather small, requiring a power of about 300 linear to render their forms and proportions distinctly. The interstitial membranes are abundantly supplied with acerate spicula irregularly dispersed, and of the same size as those of the dermis. I am indebted to m y friend Commodore Parish for this interesting species. He obtained it from the Straits of Malacca. DESMACIDON VENUSTA, Bowerbank. Sponge sessile, fistulous; fistulse comparatively large and open. Surface smooth and even. Oscula simple, within the fistulse. Pores inconspicuous. Dermal membrane pellucid, abundantly spiculous, reticulated ; rete unispiculous, very regular and beautiful; areas mostly triangular, rarely quadrangular ; spicula acerate, short and stout, same size as those of the skeleton. Skeleton-rete very diffuse and irregular ; fibres slender and compact; spicula small, short, and stout. Interstitial spaces filled with beautiful masses of unispiculous reticulated structure ; spicula same as those of the fibrous skeleton ; areas same size and form as those of the dermal membrane. Colour pale ochreous yellow in the dried state. Hab. Straits of Malacca (Commodore Parish). Examined in the dried state. This sponge consists of four short stout fistulse, not quite an inch in height, the whole mass averaging about 1^ inch in breadth, and the parietes of the fistulse are about g of an inch in thickness. The structural peculiarities of the dermal membrane, when a small por­tion of it is mounted in Canada balsam and viewed with a power of about 100 linear, are remarkably regular and beautiful, and espe­cially characteristic of the species. The rete consists of an elegantly symmetrical network of single spicula, with nearly the whole of the areas of a triangular form, a quadrangular one being of rather rare occurrence ; and as the component spicula are very equal in their lengths and diameters, the result is a remarkable degree of sym­metry and beauty. The whole of the interstitial spaces within the fibrous skeleton are filled with masses of a similarly regular and beautiful unispiculous reticular structure, closely simulating that of the dermal structure ; and amidst this beautiful tissue the long, slender, fibrous skeleton meanders in various directions. Although the structural characters of this species are few and simple, the regularity and beauty of the modes of their disposition afford ex­cellent specific characters for its identification. The only species of Desmacidon with which it might possibly be confounded is D.fo-lioides, from the same locality ; but, independent of the differences of external form, the last-named species differs in the dermal mem­brane being furnished with the peculiar leaf-like arrangement of its rete, and in the interstitial spaces; the spicula are only sparingly dispersed on the membranes. In both species the spicula are of about the same length ; but those of the species in course of descrip­tion are twice the diameter of those of D. folioides.