BRITISH SPONGIAD^!. 217 



regarding which there has existed a greater diversity of 

 opinion than the present subject of investigation, and this 

 is, perhaps, in a great measure due to the singularity of its 

 habit, in selecting the perforations of lithodomus annelids, 

 and other marine animals as its habitation, and very few 

 oyster or other shells in which such perforations exist, are 

 free from this parasitical sponge, but it does not confine 

 itself to the sinnous canals thus formed ; if they happen to 

 open into the bases of large parasitic Balani attached to 

 the shell, the whole of the interior of the Balani become 

 coated with the sponge, and in the excavated stones of 

 Tenby it frequently entirely fills the smaller cavities, or 

 completely coats the larger one made by the lithodomus 

 molluscs so abundant in the surfaces of the limestone rocks 

 between high and low water-marks in those districts. 



In one specimen of the sponge in my possession, dredged 

 by Mr. King at the Scilly Islands, in the summer of 1863, 

 the shell, a single valve of a large Pectunculus, has the 

 outer surface presenting the usual abundance of circular 

 orifices, about a line and a half in diameter, from each of 

 which the sponge is protruded in the usual manner ; the 

 inner surface of the shell, which has evidently been the one 

 lying downward, is also furnished with numerous perfora- 

 tions, but as this surface has been protected by its position, 

 the sponge has varied from its usual habit, and has spread 

 itself evenly over the whole interior of the shell, and this 

 surface, about two and a half inches in diameter, was per- 

 fectly smooth and glabrous, and quite destitute of oscula, 

 as might reasonably be expected from their abundance at 

 the outer one ; the colour of this extended surface of the 

 sponge was, in its fresh condition, of a dull ochreous yellow, 

 and the only difference that appeared to exist between it 

 and the parts within the substance of the shell, was that of 

 a more abundant secretion of sarcode. This specimen 

 exhibits the largest uninterrupted surface of the sponge I 

 have ever seen ; large cavities between the layers of old 

 oyster shells and the interior of shells of dead Balani nearly 

 an inch in height, completely coated by this sponge, are by 

 no means of uncommon occurrence at Tenby, and in the 



