ANATOMY AND LIFE HISTORY OP MOLLUSCA. 159 



Though the full meaning of all the different portions of shell- 

 structure is not clear to us, yet we can infer the purpose of the 

 fibres being at right angles to each other in the different strata, 

 which is to give great strength. We see also how it is that with 

 the death of the animal the shell suffers disintegration, unless it 

 is preserved from the action of light, heat, and . moisture on the 

 animal tissue which it contains. On the coral reefs of the East 

 one sees this plainly in the ruin and destruction that falls upon 

 the hardest and most compact shells once the animal no longer 

 lives to give them animation and support. 



Let us now pass on to the consideration of other shells besides 

 Patella tramoserica, Martyn, in which 1 have observed eyes of a 

 similar nature to those on the shell surface of Chiton and Patella. 



First on the list is Acmwa septiformis, Reeve, a small shell of 

 the limpet kind belonging to a genus, which, as already stated, 

 has a gill-plume at the back of the neck, instead of a series of gill- 

 filaments all round the foot. This species is a depressed, conical 

 shell with the apex anterior and from 40 to 50 somewhat irregular 

 and depressed ribs. These ribs are sometimes slightly undulating 

 and as they have dark lines between them, this gives the external 

 aspect of the shell an appearance of tortoise-shell. The same lines 

 of colour are thickened and bifurcate at the larger lines of growth ; 

 so that when held against the light, the colouring is light brown, 

 clouded with very dark spots and undulating lines. The inside 

 of the shell is not nacreous, or at least not so conspicuously so, as 

 the species of Patella we have been dealing with last. There is a 

 "bluish-white lining inside, except at the spathula and margin. 

 The latter is but slightly undulated by the ribs, and is variegated 

 at these points with spots of much darker brown colour. The 

 surface of the shell does not present the same symmetrical 

 arrangement of the eye-points as that which is found in the last 

 species. The surface is very closely and irregularly pitted all over 

 with minute depressions, surrounded by a ring of pigment. In 

 the centre of this is the eye, always of minute size with a small 

 dot in the centre, and lying at the bottom of the depressions spoken 

 of. The eyes themselves are extremely difficult to see unless that 

 their presence can be always inferred from the peculiar gem-like 

 sparkling of the crystalline corneas. They are so closely packed 

 together and so minute that it is utterly impossible to form an 

 estimate of their numbers except near the margin. I have done 

 no more in the case of this shell than merely ascertain the presence 

 of these shell-eyes, and have not as yet made any experiments by 

 subjecting the shell to the action of re-agents, or more closely 

 examined the organs themselves. 



Siphonaria diemenensis, Quoy, is another of the conical shells 

 which will amply reward the observer who examines it for the 



