62 POPULAR BRITISH CONCHOLOGY. 



their shells present great variations in shape and sculpture, 

 but all have the hinge external. Not only the species of 

 different genera, but even the individuals of the same species, 

 as we shall presently see, differ from each other in their ha- 

 bits of life. The genera are as follows : — 

 I. Tapes — has two moderate-sized fringed siphons, divided 

 half-way; a large, compressed, tongue-shaped foot, 

 with a groove in which a byssus is fixed, so that the 

 animal, when not in motion, or when not sufficiently 

 fixed in his cavity, can secure himself by ancJwring 

 himself to any localities he may affect. The shell is 

 oval, and, like the Venus, has two or three teeth in 

 each valve, close to the apex. Many of the Tapes are 

 found in holes of rocks, in which they have lived, and 

 have become very irregular in their growth, so much 

 so, that it is in many cases difficult to say, with regard 

 to individuals, whether they belong to Venus or Vene- 

 TujJis. This genus is represented in our seas by the 

 following species : — 

 Tajoes 'Piillastra or Venus jperforans : shell rather oval or 

 oblong, squarish at the ends, very finely striated in 

 both directions, and sometimes with strong ridges, or 

 laminae, at the hinder end. 



