LEPAS BARNACLE. 207 



erted in affording it a safeguard. This consists 

 of a very efficient operculum, composed of four 

 testaceous pieces, moveable at pleasure, and ar- 

 ticulating with the sides of the shell, sometimes 

 near the hase, sometimes towards the middle. 

 The union of these valves forms a pointed cone, 

 which completely covers the opening at the apex, 

 and protects the mollusk, who can open it at plea- 

 sure to put out its arms, and draw in food. The 

 increase in the height of these shells is clearly in- 

 dicated 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 Linnsean 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 furnished 

 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 uni- 

 ted by a membrane ; the form of the shell is that 

 of a flattened cone ; at the base is the tubular 

 flexible peduncle, by which the shell is attached 

 to marine substances. 



* Plate X. figure 7. 



