with descriptions of new Species. 323 



On the coast of Nortbumberland the surface of ahnost every 

 piece of limestone near low-water mark is riddled by Cliona : old 

 shells, whether univalves or bivalves, are filled with it ; it inha- 

 bits nullipores; and in southern latitudes it buries itself in corals. 

 Its ravages are very extensive and appear to be rapidly effected. 

 I have seen half-grown living oysters with Cliona extending from 

 the umbones almost to the ventral margin, and in one or two 

 instances it even reaches that margin. In these cases it is evi- 

 dent that the growth of the sponge must have been more rapid 

 than that of the shell ; for the work of destruction could not 

 commence until the oyster had attained to some size ; and had its 

 growth been even equal to that of the sponge, the shell ought to 

 have reached its full development before the sponge had gained 

 the lower margin. 



When a shell is once attacked, the operations of these crea- 

 tures never cease until they ha^ e extended throughout its entire 

 substance. The middle portion soon becomes almost completely 

 excavated, small pieces only remaining to divide the chambers or 

 branches. A thin plate is left on the outer and inner surfaces 

 to protect the parasite ; and even these plates are ultimately rid- 

 dled with numerous circular holes, which are the only indication 

 of the work of destruction beneath, until some slight external 

 influence ruptures the protecting walls, or the increasing growth 

 of the tenant bursts them asunder ; when the whole system of 

 elaborately wTOught chambers becoming exposed soon gives way, 

 and Cliona, Sampson-like, perishes amidst the ruin produced by 

 its own energy. 



The excavating sponges abound in the Tropics, where they will 

 keep in check the rapid increase of calcareous matter. The coral 

 reef is built up by particles, and so by particles will it be reduced 

 by the antagonism of these ever-working, all-pervading beings : 

 the huge massive Tridacna falls in pieces subjected to the insi- 

 dious encroachments of Cliona ; and the limestone rock, almost 

 bidding defiance to elemental influences, crumbles beneath the 

 touch of this the lowest of animated beings. 



It is difficult to say whether certain species of these parasites 

 confine their ravages or not to certain shells or other calcareous 

 bodies, though the fact of twelve species occurring in a single 

 individual of Tridacna would appear to contradict such an opi- 

 nion. Three or four distinct species are likewise found in the 

 common oyster, and one of them occurs in limestone : Fusus an- 

 tiquus has also supplied three good species. On the other hand 

 Cliona radiata would appear to be confined to Triton variegatus, 

 in two or three specimens of which it occurred abundantly; 

 Murex regius is frequently affected by the operations of Cliona, 

 and always, as far as I have been able to ascertain, by the same 



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