324 Mr. A. Hancock on the Excavating Poivers of Sponges, 



*species. And the three individuals of C. corallinoides that I have 

 procured are buried in as many specimens of Pecten maximus. 

 All these cases, however, may arise from similarity of locality, 

 and not from any partiality to the species. 



The boring sponges,, as far as I have examined them, are 

 branched, or are composed of lobes united by delicate stems ; 

 and all more or less anastomose according to the species : many 

 of them are beautifully arborescent and of great delicacy*. They 

 all bury themselves in shells or other calcareous bodies, and 

 communicate with the water by papillse or oscula protruding 

 through circular holes in the surface of the containing substance 

 or matrix. In dead shells the papillae pass through both surfaces, 

 but in living ones rarely penetrate the innermost layer, though 

 occasionally they do so. When a mollusk is thus wounded it 

 deposits calcareous matter over the orifice, and generally succeeds 

 in excluding the intruder. The species vary considerably in form, 

 and in Cliona might be divided into two or three distinct groups. 

 In some the branches are almost linear, and anastomose only to 

 a very slight degree ; others form a complete network with the 

 meshes so small that very little of the matrix remains between 

 the branches ; some have the branches moderately lobed ; and 

 others again have the lobes large and crowded upon each other 

 in all directions, and united by fine, very short stems. In most 

 the terminal twigs are very minute, and exhibit in a decided 

 manner the mode of growth. In C. gracilis, for example, we per- 

 ceive that they are cylindrical, and divide dichotomously, and 

 that afterwards they augment in thickness gradually and pretty 

 regularly, there being^only slight indications of a lobed structure. 

 In C. corallinoides, PL XV. fig. 1, the twigs are excessively mi- 

 nute, passing onward for some distance through the sound shell ; 

 and as they increase tkey become gradually lobed, the lobes ulti- 

 mately attaining considerable size and becoming quadrate. This 

 mode of growth is common to a great number of species : in some 

 it is beautifully modified, as we see in C. spinosa, PL XIII ► fig. 5 ; 

 here the terminal twigs are mostly short and pointed, resembling 

 spines thrust out from all sides of the close-set lobes > which 

 spines or twigs in their turn swell out and become lobes. But 

 of all the excavating sponges, Thoosa cactoides, PL XIII. fig. 1, 



* Dr. Johnston describes C. eelata as " without beauty or definite foi'm ;" 

 but the specimens he examined may have been of abnormal growth, result- 

 ing perhaps from the entire destruction of the substance which bad inclosed 

 them. The Doctor's species however appears to be distinct from the C. eelata 

 of Grant, judging by the spicula, which, according to the figures of them by 

 Mr. Bowerbank, are perfectly straight. In the species described by Pro- 

 fessor Grant they are stated to be "slightly curved and a little fusiform, in 

 the middled' 



