Lamellibranchiii . 



45 



extensible as 'siphons', which usually act as conduits for the 

 admission of water into the branchial cavity and for the expulsion 



Fig. 38. 



. ^Ln<>^«"> - t ^J!^. *t'-t'» t( ^A'M'tl'i 



A Ship-worm, Teredo navalis. 

 e.s. Exhalant siphon. /. Foot. i.s. Inhalant siphon, p. One of the pallets. 



••>•. One valve of the shell. 



Fig. 39. 



Y' Uk / 



of waste products. Yolclia (among Protobranchs), Tellina, 

 Psammobia, the Veneridae, and Teredo (Case 202) are examples 

 of siphonate forms. In Teredo the siphons 

 are enormous and allow the animal to 

 burrOw very deeply into wood. 



The Tridacnidae (Cases 195, 196) contain 

 the largest living Lamellibranchs, Tridacna 

 gigas, the Giant Clam, sometimes weighing 

 over 500 lb. 



Many of the tiolenidqe, or Razor-shells, 

 possess very elongated shells, and are re- 

 markable for the great development of the 

 foot, which can be pointed or contracted 

 as may be required for burrowing into sand. 

 By means of this powerful foot the animals, 

 when disturbed, bore with such rapidity 

 and to such a depth that their capture is 

 a matter of great difficulty. 



The Pholadidae, or ' Picklocks ', are very 

 remarkable molluscs having the power of 

 boring into rock, timber, &c. The shell is 

 strong and prickly and is used to enlarge 

 the hole as the creature grows. The common 

 Pholas dactylus (Fig. 3(3) of our own shores 

 has been found in slate-rocks, mica-schist, 

 coal-shale, sandstone, chalk, marl, peat, 

 and Avood. These animals are brightly 

 phosphorescent. Certain species are used 

 as food at many places on the shores of 

 the Mediterranean. 



The Teredinidae, or Ship-worms, are also 

 borers, but do not perforate rocks. They 

 arc principally wood-borers, and they cause 

 considerable damage to submarine timber 

 structures. 



The habits and structure of these and other wood- and stone - 



0:t 



vm 



^ 



EP 



Watering-pot Shell 

 ( BrecMtes nn/i iiifrr). 



Case 20:5. 



a. bivalve shell of the 



very young animal. 



