286 GASTEEOPODA. 



as somewhat to resemble in its shape the human ear, 

 whence the origin of the name. The circumference 

 of the foot, and the sides of the head of the living 

 animal, are decorated witli elegant fringes, and the 

 shell is likewise perforated with a row of apertures 

 through which gorgeously-coloured filaments are 

 protruded: these apertures also serve for the free 

 admission of water to the branchial chamber. The 

 mouth is a short proboscis. 



The Key-hole Limpets {Fissurella) very much re- 



FlG. 225. — FISSURELLA RETICULATA. 



semble the common Limpets of our coast, and in like 

 manner are provided with a plain conical shell, 

 Avithout any spire, which spreads over the middle of 

 their back. They differ from the Limpets, however, 

 in having the shell perforated at its apex for the 

 purpose of admitting the water into a branchial 

 chamber in which pectinated gills are lodged. 



Order Tectibranchiata. ^ 



The Grasteropods belonging to this order have 

 their branchias arranged along the right side of the 

 body, or on the back ; they are always in the form of 

 leaflets more or less divided, but not symmetrical : 

 they are protected by a sort of roof, formed by a 

 prolongation of the mantle. These animals are for 

 the most part naked slugs ; but some have a small 

 shell concealed in the mantle, and others have a 

 conspicuous one of considerable size : we select as an 

 example of this order 



* Tectus, covered ; branchise, gills — covered-gills. 



