| OCR Text |
Show 1876.] DR. j. s. B O W E R B A N K O N T H E SPONGIADJE. 773 RAPHIODESMA RADIOSA, sp. nov. (Plate LXXXI.) Sponge irregularly rameous ; branches rather slender. Surface uneven and irregular, both strongly and minutely hispid. Oscula simple, dispersed. Pores inconspicuous. Dermal membrane pellucid, abundantly spiculous, reticulated ; spicula of the rete of the same form as those of the skeleton. Tension-spicula acuate, slender, few in number ; retentive spicula dentato-palmated inequianchorate, congregated in rosette-shaped groups, rather numerous, and, rarely, simple and contort bihamate spicula. Skeleton-fasciculi numerous, abundantly spiculous; spicula acuate, rather stout. Interstitial membranes sparingly furnished with the same tension- and retentive spicula as those of the dermal membrane. Colour, in the dried state, light grey. Hab. Savanilla, South America. Examined in the dried state. I received this very remarkable sponge from Mr. Moore, of the Liverpool Free Library and Museum, for examination and description. He informed me that it was collected at Savanilla, a sea-port town on the South-American coast, latitude 11° S., longitude 75° W . What has been the nature of the basal attachment of this sponge is very doubtful; as it is at present, it appears as if it had been broken off immediately above the basal attachment. The length of the specimen represented by the figure iu Plate L X X X I . is 19 inches ; and its diameter averages •§• of an inch at three inches above its present base. The whole of the surface is very uneven, and it is irregularly studded with numerous conical projections about a line or a line and a half in height; and these appear to be produced by the occasional projection of the minute irregular ramifications of the young and immature branches of the sponge at a. Beside these conical organs, the surface is abundantly but very minutely hispid ; and this affords an excellent specific character. It is produced by the gradual radiation of the distal extremities of the fasciculi of the skeleton immediately beneath the dermal membrane, as represented by fig. 2, Plate L X X X I . This singular provision of nature for the defence of the dermal structure of the sponge is very remarkable and especially characteristic; but it can only be seen to advantage in a thin section of the sponge made at right angles to the surface, mounted in Canada balsam and viewed as a transparent object with a microscopical power of about 100 linear. The amount of the projection of the distal terminations of the spicula of these fasciculi scarcely exceeds about one third or half the length of a single spiculum ; but they form a most efficient protection to the dermal structure of the sponge. The dermal membrane affords especially valuable specific characters independently of the remarkable radial groups of defensive spicula which pass through its structure, lt is very pellucid; and the rete with which it is furnished is strongly but irregularly produced, and the areas are large and mostly modifications of triangular or quadrangular forms ; and where any portion of it terminates PROC. ZOOL. Soc-1876, No.LI. 51 |
