LEPAS BARNACLE. 207 



had not the compensatory providence of the 

 Creator been exerted in affording it a safeguard. 

 This consists of a very efficient operculum, com- 

 posed of four testaceous pieces, moveable at 

 pleasure, and articulating with the sides of the 

 shell, sometimes near the base, sometimes to- 

 wards the middle. The union of these valves 

 forms a pointed cone, which completely covers 

 the opening at the apex, and protects the mol- 

 lusk, who can open it at pleasure to put out its 

 arms, and draw in 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 mollusk 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 the tubular flexible peduncle, by 

 which the shell is attached to marine substances. 



* Plate X. figure 7. 



