PATELLA LIMPET. 121 



is connected with a different formation of the 

 animal, whose gills are situated near the hole 

 through which it receives the needful supply of 

 water; these now belong to the modern genus 

 Fissurella ; others which have a fissure or notch 

 at the margin are called Emarginula. In some, 

 the apex is very retuse ; whilst in others it is 

 pointed and elegantly recurved.* 



This genus is peculiarly interesting to those 

 who love to trace the regular, but almost im- 

 perceptible gradations existing in the scale of 

 nature. The species with the recurved apex 

 seem to form the link which connects the Patellae 

 with spiral shells, whilst the other species, where 

 there is no trace of any volutions, present the 

 intermediate grade between them and the shells 

 entirely destitute of spires. 



The animal of the Patella has a large fleshy 

 proboscis, and two tentacula, with the eyes on a 

 small elevation at their base ; the mouth has 

 cartilaginous plates for the mastication of its 

 food. It has a ventral foot, fleshy, and fur- 

 nished with numerous muscular filaments, which 

 uniting on the upper part of the mantle, form 

 a strong muscle by which the body adheres to 

 the shell. By the action of this muscle, the shell 

 can be brought close to the surface to which the 

 foot adheres, or removed to a distance : and it 

 is by means of this instrument, that the animal, 

 when desirous of changing its situation, is able 



* Plate VI. figure 1. 



