PELECYPODA. 



43 



disturbed, bore with such rapidity and to such a depth that their 

 capture is a matter of great difficulty ; and even when seized they 

 hold on so tightly that at times they suffer their foot to be torn off 

 rather than be captured. They not only burrow in sand, but also 

 have the power of darting through the water, like the Scallops, 

 Solens were considered a dainty dish by the ancient Greeks, and 

 numbers are still eaten by the poorer coast-population of this 

 country and abroad. 



The Pholadidce,, or Piddocks, are very remarkable shells, of an Cases 201- 

 unusually complicated structure, some having the power of boring ^'^^• 

 into rocks, wood, mud, sand, etc. Their shells are white, adorned with 

 prickly sculpture, and, although thin, are strong- The foot is believed 

 to be the principal excavating instrument, but the shell appears 

 to be used as a file to enlarge the hole as the creature grows. 

 These animals are brightly phosphorescent ; and certain species are 

 eaten at many places on the shores of the Mediterranean. They 



Piddock, or Borer (Pholas dactylus). (From the British coast.) 



1. Animal in the shell: a, foot; b, siphons; c, inhalant orifice; d, exhalan 



orifice. 



2. Shell : e, accessory valves or plates. 



appear to be indifferent as regards the material they bore into ; for 

 the common Pholas dactylus (Fig. 36) of our own shores has been 

 found in slate-rocks, mica-schist, coal-shale, hew red sandstone 

 chalk, marl, peat, and submarine wood. The siphons are long in the 

 Piddocks, united except near the end, and enclosed in tough skin. 

 The species are world-wide in their distribution, and several are 

 found fossil in some of the Tertiary and older formations. 



The Teredinidce,, or Ship-worms, are also borers, like the Pholads, Case 202. 

 but do not perforate rocks. They are principally wood-borers ; the 

 large Kuplius arenarius, which is an exception, living buried in the 

 sand. The ship-worm has a long worm-like body, from 6 to 12 



