HRITISH SPONGIADjE. 357 



acuate through every imaginable variation of the spinulate 

 form. 



This sponge is undoubtedly Dr. Johnston's Halichondria 

 celata, " var. a. massive and wide." The small piece I re- 

 ceived in a letter from my friend for the purpose of the 

 delineation of its spicula which are represented by fig. xiii, 

 page 127, of his 'History of British Sponges/ sufficed only 

 for the purpose for which it was transmitted, and it is not 

 a matter of surprise that it should have been confounded 

 with Dr. Grant's Cliona celata, the spicula of the two 

 species being so very similar in size and form ; but in other 

 respects, as in the form of the skeleton structures, the 

 species are widely separated from each other. 



Diplodemia, Bowerbank. 



1. Diplodemia vesicula, Boioerbank. 



Sponge. Sessile, massive. Surface, Oscula. Pores, and 

 Dermal membrane unknown. Primary skeleton ; fibre 

 branching and inosculating, smooth, cylindrical ; hetro- 

 spiculous ; spicula few in number, acerate. Secon- 

 dary reticulated spiculous skeleton ; filling up com- 

 pletely the interstices of the primary fibrous ones ; 

 rete rarely more than unispiculous ; spicula same as 

 those of the primary skeleton. Ovaries attached to 

 the primary skeleton, oval or ovoid, membranaceous, 

 thin, abundantly spiculous ; spicula dispersed or sub- 

 fasciculate ; acerate, equal in size and proportions to 

 those of the skeleton. 



Colour. t- Dried, gray. 



Habitat. Shetland, Mr. Barlee. 



Examined. In the dried condition. 



This remarkable sponge was obtained by my friend Mr. 



