187C] DR. J. S. BOWERBANK ON THE SPONGIAD.E. 7/3 



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, con- 

 gregated 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. 

 Hob. 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 in Plate LXXXI. 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 irregularlv 

 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 LXXXI. 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 micro- 

 scopical 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 charac- 

 ters independently of the remarkable radial groups of defensive 

 spicula which pass through its structure. It is very pellucid ; and 

 the rete with which it is furnished is strongly but irregularly pro- 

 duced, 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 



