BRITISH SP0NGIADJ5. 139 



Habitat. St. Katherine's Cave, Tenby. Rocks off' 

 Hastings at low water ; Gnliot Caves, Sark ; Sennen Cove, 

 Land's End, Cornwall, J. S. Bowerbank. 



Examined. In the living state. 



This sponge occurs abundantly in the small cave about 

 the middle of the north side of St. Katherine's Island, 

 Tenby ; accessible without a boat only at very low tide. 

 Its appearance is that of a small patch, from one to two 

 inches in diameter, of dark clot of blood adhering closely to 

 the surface of the rock, and it can be obtained only by 

 cutting away' the piece of stone to which it adheres. It 

 rarely exceeds about half a line in thickness. Its extreme 

 thinness readily distinguishes it from the deep red coloured 

 sponge, Chalina seriata, which occurs abundantly along 

 with it in that cave, and which is so thick as to be easily 

 removed from the rock with a knife. 



In the living condition I could not detect the oscula, but 

 in the dried state, by the aid of a two inch lens, they 

 appear to be numerous, and dispersed equally over the 

 surface of the sponge. I could not find the pores. 



The columns of keratode rarely exceed in height the 

 length of one of the large skeleton spicula, and are frequently 

 not more than half or a third of that length ; they never 

 appear to anastomose with each other, but are united at 

 their bases by a uniform thin stratum of keratode or con- 

 densed membranous basal tissue, in which is imbedded, 

 without order, numerous slender sub-clavato-acuate spicula, 

 with a few tricurvato-acerate ones, and from the bases of 

 the columns we find occasionally a single entirely spined 

 sub-clavato-attenuato-acuate defensive spiculum projected. 

 The dermal membrane also abounds with the same descrip- 

 tion of spicula that we observe in the basal stratum. It is 

 situated immediately above the apices of the keratose 

 columns, and in the intervals between them it is supported 

 and strengthened by the numerous long slender tension 

 spicula which cross each other in various directions ; the 

 large terminal spicula passing through it powerfully 

 protects it from injuries from without. 



