MULTIVALVES. 



had not the compensatory providence of the Cre- 

 ator been exerted in affording it a safeguard. 

 This consists of a very efficient operculum, 

 composed of four testaceous pieces, moveable 

 at pleasure, and articulating with the sides of 

 the shell, sometimes near the base, sometimes 

 towards the middle. The union of these valves 

 forms a pointed cone, which completely covers 

 the opening at the apex, and protects the mol- 

 lusca, who can open it at pleasure to put out 

 their arms, and draw in their food. The increase 

 in the height of these shells is clearly indicated 

 on their lateral valves, whilst at the base are 

 traces of extension in width ; it is probable that 

 at each period of growth, the animal disunites its 

 valves and connects them again, having added 

 the necessary portion to their size. 



The Linnaean name of Lepas is now confined 

 to the division containing the Peduncled shells.* 

 The mollusca inhabiting them may be considered 

 as different from those of the Balanus, because 

 the tube which supports the shell is in fact a part 

 of the animal; it is organized, living, and fur- 

 nished with muscles which give the Lepas the 

 power of regulating its movements. The shell 

 is composed of five valves, two on each side, and 

 one long and narrow on the dorsal ridge ; these 

 valves are united by a membrane ; the form of 

 the shell is that of a flattened cone ; the base is 

 sustained by a tubular flexible peduncle, attached 

 to marine substances. 



* Plate X. figure 7. 



