240 Mr. A. Hancock on the Boring of the Mollusca into Rocks, 



liant points ; and on increasing the pressure, comparatively large 

 imbedded, crystalline bodies are revealed (PI. VIII. figs. 6 and 7). 

 They are very numerous and of various sizes and shapes, chiefly 

 five- and six-sided, but not by any means regularly so : they all 

 agree in having one or more elevated points near the centre. It 

 was these points, apparently, that were seen in the first instance 

 shining on the surface. These bodies are highly refractive, and 

 are for the most part pretty regularly distributed over the whole 

 convex surface of the foot, but are occasionally congregated into 

 masses. Similar crystalline bodies are likewise imbedded in the 

 edges of the mantle surrounding the foot. 



In Pholas the same appearance is presented both in the foot 

 and in the surrounding edges of the mantle. When the anterior 

 convex surface of the foot of P. crispata, for instance, is removed 

 and examined with the aid of the compressor, it is found to be 

 studded over with minute dark spots, each emitting a brilliant 

 point of light from the centre. On using a higher magnifying 

 power the whole surface is seen to be crowded with crystalline 

 bodies, some dark-coloured, others perfectly transparent, and re- 

 sembling in shape and character those of Teredo ; but most com- 

 monly drawn together into little bundles, and very brilliant : 

 they are sometimes also gathered into considerable masses. These 

 bodies in some specimens are quite colourless ; but when of a 

 dark reddish brown, which is not uncommon, they have at first 

 sight a glaudular appearance, especially when the imbedding 

 tissue is a little thickened about them, which frequently happens. 

 The dark spots of a glandular aspect observed by Professor Owen 

 in the outer dermoid layer of the mantle of Clavagella may pro- 

 bably prove to be similar crystalline bodies. 



Saxicava rugosa has also the anterior portion of the animal 

 abundantly provided with crystalline bodies like those already 

 described (figs. I and 2) ; but they are for the most part larger 

 and stouter, and are likewise frequently associated in groups. 

 They are highly refractive, perfectly colourless and of a glassy 

 purity ; and are imbedded in a thinnish epidermis, which is firmly 

 attached in the living state to the thickened portion of the mantle, 

 but is easily pealed off when the animal has been some time in 

 spirit. The thickened portion of the mantle of Gastrochana is 

 also furnished with similar crystalline bodies, but from the want 

 of specimens I have not been able to examine them in this spe- 

 cies so fully as is desirable. 



The foot and mantle of Patella vulgata likewise exhibit these 

 brilliant bodies ; but in this species they are smaller and less 

 robust than usual. In the species which has been mentioned as 

 boring in the large Patella from the coast of America, they at- 

 tain, however, a high degree of development. I fortunately ob- 



