BRITISH SPONGIADJE. 61 



2. Polymastia bulbosa, Bowerbank. 



Sponge. Sessile, basal mass bulbous, apex of bulb termi- 

 nating in a single fistula. Fistula gradually atten- 

 uating from the base to the bluntly conical apex. 

 Surface even, minutely hispid. Oscula terminal on 

 the cloacal fistula. Pores inconspicuous. Dermis of 

 basal mass thin. Dermal membrane pellucid ; dermis 

 of the basal mass furnished abundantly with minute 

 spinulate external defensive spicula, based on the 

 external surface, irregularly dispersed. External 

 defensive spicula of fistula same as those of basal 

 mass ; congregated more especially above the lines of 

 the skeleton tissues. Skeleton. Fasciculi rather widely 

 apart, loosely compacted; spicula acuate, large and 

 long. 



Colour. Alive, and in spirit, cream white. 

 Habitat. Shetland, Mr. C. W. Peach. 

 Examined. In spirit, as it came from the sea. 



This remarkable species was dredged at Shetland, in 

 1864. Its form is very much like that of a young onion 

 just beginning to develop its bulb. The basal mass is 

 seven lines high to the base of the fistula, and its greatest 

 diameter is six lines. The terminal fistula is nine lines in 

 length, and one and a half lines in width, near its base; 

 it is in a closely collapsed state, but in opposite directions, 

 at different parts of its length, and it gradually decreases 

 in diameter from its base to its apex, terminating in a 

 bluntly conical form. The base of the bulb is firmly 

 cemented to the remains of a large Balanus, in company 

 with a young specimen of Dictyocylindm hispidus, the base 

 of which spreads over a part of the shell, while that of 

 P. bulbosa does not extend in the slightest degree beyond 

 the point of its attachment. 



The solitary fistula and the general aspect of the struc- 



