346 



The (jcean. 



consolidated and armed with three spines : the sides 

 have a narrow fissure through which a semi-trans- 

 parent membrane protrudes. The animal is furnished 



GLASS SHELLS. (Ilt/alca tridentata, UTid Cleodora pyramidata.) 



with a wing or fin on each side, which it uses as oars. 

 A kindred species ( Cleodora cusjndata) is of extreme 

 delicacy and beauty. The shell is glassy and colour- 

 less, very fragile, nearly in the form of a triangular 

 pyramid, with an aperture at its base, from which 

 proceeds a long and slender glassy spine ; and a 

 similar spine projects from each side of the middle 

 of the shell. The animal is like the preceding ; but 

 the hinder part is globular and pellucid, and in the 

 dark vividly luminous, presenting a singularly striking 

 appearance, as it shines through its perfectly trans- 

 parent lantern. Both of these are found floating in 

 great numbers on the surface of the sea. 



Among the sea-shells which attain a large size in 

 these seas, the Giant Clamp [Tridacene g^gas) stands 

 pre-eminent. It is found in abundance on the coasts 

 of Sumatra, as well as of other islands, attached to 

 the rocks by a strong cable. This, which is called 

 byssus, is formed of many tough threads, but slightly 

 filastic, spun by the animal, or rather, cast in a 



