324 



PH0LADI2LE. 



usually with calcareous plates which maintain the valves in 

 position. 



The Pholadidce are found in most parts of the glohe, 

 living in calcareous rocks, clay, or submerged wood. Fix- 

 ing their bodies by means of their sucker-like foot, they 

 are enabled to perforate most substances softer than their 

 shells by the mechanical, rotatory action of the valves, 

 assisted by the front portion of the mantle, which is 

 strengthened for the purpose by silicious granules. The 

 grooves of the rasp-like asperities of the shell are visible 

 on the walls of their burrows, and M. Cailliaud has in- 

 geniously demonstrated the power of their mechanical at- 

 trition by forming, himself, similar perforations in lime- 

 stone by carefully rotating the valves of a Pholas under 

 water. The burrows are usually vertical and symmetrical, 

 and are enlarged by means of the foot and portions of the 

 siphons and mantle which are often furnished with a rough 

 epithelium for the purpose. On account of their burrow- 

 ing habits these animals are often very destructive to sea- 

 walls, piers, breakwaters, and other structures under water. 

 In villages along the shores of the Mediterranean the 

 Pholades are used as food. They are vividly phospho- 

 rescent in the dark. 



Sub-fam. PHOLADIN^E. 



Animal clavate. Siphons unprovided with shelly styles 

 or palettes. Umbonal muscle protected by one or more 

 shelly, accessory valves. 



Living in a cavity not usually lined with a regular shelly 

 tube enclosing the valves. 



