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Show 1874.] DR. J. s. B O W E R B A N K O N T H E SPONGIAD^E. 299 multiangulated cylindrical retentive spicula; they are so minute as to require a power of five or six hundred linear to render their forms distinctly to the eye. The number of angles in these spicula vary from two or three to six or seven; and in some cases the angulation is very distinctly and regularly produced. From the thin coating nature of the sponge the skeleton-arrangement is not so readily demonstrable as in many other species of the genus. The fasciculi are abundantly spiculous and very compactly constructed. The bases of the spicula are all coincident and proximal, while all the apices are distal as regards the direction of the fasciculi. The interstitial membranes are in many parts literally crowded with the arborescent elongo-subsphero-stellate retentive spicula, and they are also dispersed in considerable quantities amongst the ovaria in the dermal crust. These spicula are singular and very characteristic organs. The specimen figured is a very fully developed one. They vary in degree of development to a very considerable extent; and in some the central mass is very thin and elongate. In the dermal crust of the sponge none but fully developed ovaria are to be found ; but they are dispersed in considerable numbers on all parts of the interstitial membranes, and in every stage of development from an elongately oval loosely aggregated mass of very minute spicula to the compact and fully matured organ. The spiculous structure of these ovaria is very much finer and more minute than in any other species of Geodia with which I am acquainted. GEODIA IMPERFECTA, Bowerbank. (Plate XLVI. figs. 6-13.) Sponge massive, tuberous, sessile. Surface smooth. Oscula simple, minute, dispersed. Pores inconspicuous. Dermal membrane unknown. Skeleton-fasciculi rather loosely constructed ; spicula subfusiformi-acerate, rather stout and short. Connecting spicula attenuato-patento-ternate; radii rarely perfectly developed, distal terminations recurved, not very numerous. Interstitial membranes- retentive spicula sphero-stellate with cylindro-subfoliate radii, numerous; and attenuato-stellate, variable in form, occasionally subsphero-stellate more or less. Ovaria oval, depressed. Colour in the dried state cream-white. Hab. South sea. Examined in the dried state. I obtained four specimens of this species from a dealer in objects of natural history ; they are each attached to the basal portion of a specimen of Oculina rosea from the South Sea ; the figured specimen is the largest of the four. The whole of them possess the same description of tuberous massive form ; the smallest two did not exceed an inch in length by about half an inch in breadth. The oscula are so small as to require the aid of a lens of two inches focus to render them readily apparent. I could not find any remains of the dermal membrane on either of the specimens. The connecting- 20* |
