44 



SHELL GALLERY. 



Ficr 



inches in length, which is more or less enclosed in a thin shelly tnbe 

 or sheath. The true bivalved shell is at the thicker end, and pro- 

 tects the mouth, labial palps, the liver, and 



other internal organs. At the opposite, or 



more slender, end of the animal, the mantle 



is produced into two small tubes, one of which 



conveys the water to the gills, whilst through 



the other the water is expelled, charged with 



the woody pulp excavated by the foot. At 



the end there is a pair of pallets, or paddles 



as they are sometimes 



termed, which are probably 



used as a means of defence, 



in closing the shelly tube 



after the contraction of the 



siphons. 



These animals are 



most destructive to 



wood which is not pro- 

 tected by metal, and 



when once attacked, it is 



soon riddled through and 



through. They work either 



with or across the grain, 



and although the holes 



may be all but touching, 



they seldom appear to run 



into one another. 



The " Watering - pot 



shell " (Brechites),. of the 



family ClavageUidce, is a 



very remarkable structure, 



and unlike the shell of an 



ordinary bivalved mollusc. 

 On looking carefully, however, near the per- 

 forated end (the rose), two small valves will be 

 seen imbedded in the surface. These shells are 

 found Avith the rose downwards buried in mud 

 or sand at low water on the shores of the Indian and Pacific 

 Oceans. 



Sliip-worm 



(^Teredo norvegica). 



Case 202. 



«, animal, removed 

 from its shelly tube : 

 p, 2^, pallets ; s, cx- 

 halant siphon; s', in- 

 halant siphon. 



b, c, ditFerent aspects 

 of the shell. 



Watering-pot Shell 

 (^BrecMtes vaginifer). 



Case 203. 

 a, bivalve sliell of 

 the very young 

 animal. 



