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sion of by a species of Barnacle (Balanus), which forms a promi- 

 nence on its surface, and is covered externally with a coat of the 

 sponge. 



Xenospongia patelliformis (PI. XII.). 



Hah. Torres Strait. 



The particles of sand forming the lower coat of the sponge are as 

 if they were imbedded in a kind of plaster, having a smooth uniform 

 surface, exactly as if the sand had been well mixed with a small 

 quantity of fluid mortar and then cast upon a smooth body. 



The whole under surface is not perfectly smooth, but with more 

 or less distinct impressed lines or concavities placed parallel with 

 the circumference, showing the periodical increase in the size of the 

 sponge. 



There is scattered over the under surface of the larger specimen a 

 few larger dark-coloured stones and a few fragments of shells, which 

 give a variegated appearance to the coat. The larger specimen, after 

 it had reached a certain size, made an irregular growth on one of the 

 sides, forming two rounded lobes which overlap each other, while 

 the whole front retains the concave conical shape. 



The lobe, which is expanded on the under surface of the other, 

 is fringed with a continuous series of very close tufts of silky spicula. 

 I have no doubt, as the bases of these tufts are to be seen on the rest 

 of the margin, that similar tufts occupy the whole edge of the 

 sponge in its perfect state, and have been rubbed off ; they have been 

 retained in this place, because it is better protected from external 

 injury than the other part of the sponge. 



In the larger specimens the grooves are much more irregular, as 

 well as more abundant and more crowded than in the smaller one ; 

 and in some few instances they appear to arise in the surface inde- 

 pendent of any connexion with the other grooves, which is not the 

 case in the smaller example. 



In the same specimen there are a few groups or rather lines of 

 oscules, situated on the surface of the sponge itself, and not placed 

 in the grooves, where all the other oscules are placed. 



In the diverging grooves the texture of the sponge seems to be 

 across the grooves, that is, parallel to the outer circumference of the 

 sponge, leaving minute square pits in the network. 



In the marginal grooves, on the contrary, the chief fibres of the 

 texture appear to be also across the groove, but that is radiating from 

 the centre towards the margin ; this appearance may probably be 

 partly, if not entirely, arising from the manner in which the sponge 

 has contracted when it dried, and may not be apparent in the fresh 

 state ; but having only a single specimen of the adult and young 

 form of the sponge, I am disinclined to soak it in water and examine 

 it in a moist state, fearing that it may spoil the specimen, which is 

 now very brittle and inclined to crack from the edge to the centre 

 of the frond. 



