112 POPULAE BRITISH CONCHOLOGY. 



Macandrei, and Jeffreysii are all that we can show in our 

 ungenial seas of that numerous class of little molluscs, 

 which abound in warmer regions, and with their glassy 

 shells sparkle near the surface of the water. The shells of 

 the two genera are perfectly distinct, that of the Hyalcea 

 resembling a bivalve, with the edges glued down, and that 

 of the Sjnralis being like a lengthened snail ; but notwith- 

 standing these differences, and others still greater, in other 

 members of the order, as to the glassy or horny test, the 

 animals are very similar, each having a pair of swimming 

 paddles likened to wings, giving them the name ''Ptero- 

 poda," or wing-footed^ and causing a distinguished natu- 

 ralist to term them " Neptune's bees and butterflies/' 



