OCR Text |
Show 1875.] DR. J. S. BOWERBANK ON THE SPONGIADcE. 295 distal extremities of the branches. The skeleton-structure of this species appears to be very irregular; but the well-produced primary lines of the skeleton unmistakably stamps it as an Isodictya. The rete of the dermal membrane is more or less irregular, and is, with its retentive spicula, very characteristic of the species. Its areas frequently exceed in width the length of a spiculum, and they vary to a considerable extent in form. The retentive spicula within them are in some of them rather numerous, while in others they are very sparingly distributed ; they are very minute and slender, requiring a power of about 500 linear to render them distinctly to the eye. In the interstitial membranes the retentive spicula are very much more numerous than they are in the dermal one ; and they are especially so in the linings of the fistulous cavities. It is very probable that hereafter this species will be found to attain a much greater altitude than the specimen in course of description. I am indebted to m y friend Commodore Parish for my knowledge of it. He obtained it from the Straits of Malacca. DESMACIDON FOLIOIDES, Bowerbank. Sponge ramous, branches inosculating. Surface smooth, but more or less spiniferous. Oscula simple, dispersed. Pores inconspicuous. Dermal membrane pellucid, spiculous, furnished with a leaf-like reticulation of minute acerate spicula. Skeleton-reticulating fibres compact and strong; areas wide and irregular. Spicula acerate, rather small and short. Interstitial membranes spiculous ; tension-spicula dispersed, same form and size as those of the dermis. Colour, iu the dried state, dull ochreous yellow. Hab. Straits of Malacca (Commodore Parish). Examined in the dried state. This sponge and a small specimen of Geodia carinata are based together on a little sandy mass; they are so closely incorporated, and so nearly resemble each other in size, colour, and form, as to be readily mistaken by a hasty observer for one species only. The sponge-stem has an irregular expansion of 4\ inches length, and has an average diameter of about 4 lines; one portion of the branches is comparatively smooth, while another portion abounds in spinous projections. The most strikingly distinctive character in this sponge exists in the dermal membrane. When a portion of it is mounted in Canada balsam and viewed with a linear power of about 100, it exhibits an appearance exceedingly like that of a portion of the skeleton of a macerated leaf of Populus nigra. There are a series of veins or long fasciculi composed of numerous minute acerate spicula meandering for considerable lengths on the inner surface of the membrane ; and the spaces between each of these are occupied by a very delicate uniserial network of minute spicula, simulating in a remarkable manner the leafy skeleton. The skeleton-rete is very open and irregular, and the fibre of which it is composed is very closely compacted ; the acerate spicula of the skeleton are very much larger |