180 BIVALVES. 



shells are irregular in their form, have a rugged 

 and laminated exterior, with one valve more con- 

 cave than the other, are generally without ears, 

 and their colour is grey or black. 



The Pectens are described as possessing asto- 

 nishing powers of locomotion, considering the 

 inferiority of their organization ; but dexterity 

 and ingenuity frequently compensate for natural 

 deficiency. They have the power of progressive 

 motion, both on land and in the water. When 

 the animal happens to be left on the shore by 

 the retiring tide, it opens its valves to their 

 full extent, and closing them with great mus- 

 cular power, is thrown forward five or six 

 inches by a sudden leap. In this manner it 

 reaches the sea ; should the weather be calm, it 

 raises one of its valves, which catching the breeze, 

 acts as a kind of sail, while the other resting on 

 the surface, supports the floating animal ; when 

 danger threatens, the shell is closed, and sinks 

 securely to the bottom of the sea. Many of the 

 Pectens possess the power of forming threads, by 

 which they anchor themselves to floating timber, 

 and by this means find protection when the sea 

 is agitated by storms and tempests. These 

 varied means of escaping danger are no doubt 

 afforded as a necessary protection against their 

 numerous enemies. The pilgrims who in former 

 days visited Jerusalem, to pay their devotions 

 at the holy sepulchre, on their return wore 

 these shells in their caps as trophies of their 

 achievement in crossing the sea for this sacred 



