1873.] DR. J. S. BOWERBANK ON CEYLONESE SPONGES. 29 



when examined microscopically. It is produced partly by the ex- 

 tension of the primary lines of the skeleton, and partly by the pro- 

 jection of single spicula, of the same size and form as those of the 

 skeleton, through the dermal membrane. I could not detect either 

 oscula or pores on any parts of the external surface ; and it is very 

 possible that inhalation takes place on the outer surface, within the 

 folds of the plications of the skeleton-tissues, and that the excur- 

 reut streams are ejected on the inner surface in a similar manner. 

 And this mode of inhalation and of exhalation is the more probable 

 as these plications are distinctly visible to the unassisted eye for 

 about half an inch downwards on the outer surface, and to twice as 

 deep on the inner one. The plications are composed of closely 

 packed parallel thin plates of the sponge-tissue, all disposed at right 

 angles to the dermal surface ; but this regular arrangement of the 

 skeleton-tissues does not seem to obtain beyond the limits stated 

 above ; the lower portions of the skeleton-structure appear to me- 

 ander in every possible direction. 



The dermal membrane does not spread uniformly over the sur- 

 faces of the sponge, but it appears to follow and encase the plications 

 of the skeleton ; and I could obtain a view of it only on the surface 

 of the plates, and on the terminations of the defensive prolon- 

 gations of the primary lines of the skeleton projected from the ex- 

 ternal surface of the sponge, when mounted in Canada balsam, and 

 with a power of about 80 linear. On those parts it was abundantly 

 supplied with the slender tension-spicula, intermixed with which 

 were a considerable number of the larger or skeleton-spicula. 



The skeleton is very strongly developed. The primary lines fre- 

 quently throw off branches which pursue their course in lines parallel 

 to the parent braneh. This habit, in conjunction with the great 

 irregularity in the size and mode of disposition of the secondary lines 

 of the skeleton, often produces a considerable amount of confusion 

 among the skeleton-structures. 



I have never observed the same singularly plicated form of the 

 skeleton-tissues in any other species of Isodictya with which I am 

 acquainted. 



Mr. Holdsworth, in his letter to me, writes :— " The dark, thick 

 cup-shaped sponge with undulated margin is not uncommon on the 

 large pearl-bank in from 6| to 9 fathoms ; and I have met with it 

 once or twice ou rough ground on other parts of the coast; it is 

 usually attached to some bit of rock, and is always, when alive of a 

 uniform bright orange-colour. It turns black an hour or two' after 

 being taken out of the water. The largest specimen I have seen 

 was about as large again as the one you have. The general shape 

 and colour are always the same." 



Haliphysema ttjbulatum, Bowerbank. (Plate VII.) 



Sponge massive, sessile. Surface minutely mamillated. Oscula 



and pores inconspicuous. Dermal membrane obsolete. Skeleton 



composed of numerous single and separate cylindrical tubuli radiating- 



trom the base to the surface of the mass; tubuli closed, termi- 



