18 JANUARY. 



probably few are aware how very elegant a creature it 

 is when tenanted by its living inhabitant, and crawling 

 at ease in clear water. The foot, on which it glides 

 with a slow but smooth motion over the surface of the 

 rock on which it habitually dwells, or, if you please, on 

 the bottom of the saucer of sea- water in which you are 

 examining it, is a broad expansion spreading out to 

 twice the superficies of the base of the shell Above 

 this is the fleshy mantle, which is so turned up as 

 closely to invest the shell, conforming to its shape, and 

 even fitting into the grooves between the ridges. This 

 mantle can be protruded, at the will of the animal, 

 so far that the two sides meet along the top of the 

 shell, and completely cover it, or it can be completely 

 retracted within the wrinkled lips beneath ; and it is 

 capable of all gradations of extension between these 

 limits. From the front of the shell protrudes the head, 

 armed with two straight and lengthened tentacles, 

 answering in function and appearance to the upper 

 pair of horns in a snail ; except that the little 

 black points which constitute the visual organs are not 

 in this case placed at the tips, but on a little promin- 

 ence on the outside of the base of each tentacle. Above 

 and between these, which diverge at a considerable 

 angle, projects the proboscis, a rather thick fleshy tube, 

 formed by a flat lamina, with its edges bent round so 



