SEA-SNAILS AND SEA-SLUGS. 223 



We must return now to certain limpet-like forms, of which 

 one, the Key-hole Limpet (Fissurella grcecd), might be easily 

 passed by as a Common Limpet that has got damaged. In 

 form and appearance the shell is not unlike the common 

 kind ; the peculiarity consists in a short and narrow slit at the 

 summit, which has suggested the name. As a living mollusk 

 it must be sought in the laminarian zone, but the empty shells 

 are to be found between tide-marks. A smaller, but not very 

 dissimilar shell, has the key-hole not on the apex, but a little 

 in advance of it. This is the Perforated Limpet (Puncturella 

 noachind). It is rarer than the last, and is to be sought on 

 the North coasts, where it lives below the twenty-fathom line. 



Yet another species is depicted in this 

 cut. It is the Slit Limpet (Emarginufa 

 reticulatd), in which the notch or slit is in 

 the fore edge of the white shell ; length of 

 slit variable. Internally the shell is thick- 

 ened near the notch, and outside it is 

 deeply grooved, so that strong ribs radiate 

 from the summit, and are themselves partly 

 cut up by lighter grooves transversely to 

 the others. It comes up to low-water mark, 

 so may be taken alive from the shore. 



There is a second British species, the Rosy- 

 ,., T . /,'/. i j SLIT LIMPET, v 



slit Limpet (E. rosed), much smaller, and 



sometimes with the slit rosy, but this is not a reliable character. 

 On our Southern shores may be found frequently on oysters 

 a shell that may be said to be the highest development of 

 the limpet type. Seen from the point of view taken for our 

 illustration, there is a long gentle curve from the mouth to the 

 beak, which is spirally twisted. The general effect is to remind 

 one of the conventional representations of the Cap of Liberty. 

 Owing to this cap-like form, it is known as the Hungarian Cap, 

 and the Torbay Bonnet (Pileopsis hungaricus). In colour it 

 varies from brown to an indefinite dirty- white hue. 



