364 THE OCEAN. 



and Indian Oceans by two or three species nearly 

 allied to it in structure, but furnished with a glassy 

 shell. One of these is named Hyalea tridentata; 



Glass Shells. (Hyalea tridentata, and Cleodora pyramidata.) 



its shell is small and somewhat erlobular, resembling 

 a bivalve without a hinge ; the hinder part being 

 consolidated and armed with three spines ; the sides 

 have a narrow fissure through which a semi-trans- 

 parent membrane protrudes. The animal is fur- 

 nished with a wing or fin on each side, which it uses 

 as oars. A kindred species {Cleodora cuspidata) is 

 of extreme delicacy and beauty. The shell is glassy 

 and colourless, 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 preced- 

 ing; but the hinder part is globular and pellucid, 

 and in the dark vividly luminous, presenting a sin- 

 gulars-striking appearance, as it shines through its 

 perfectly-transparent lantern. Both of these arc 

 found floating in great numbers on the surface of 

 the sea. 



