66 THE STORY OF LIFE IN THE SEAS. 



over the reefs, but their beauties are frequently 

 hidden, when alive, by the coal-black mantle 

 which folds back over the shell as they crawl 

 along. It must nob be supposed, however, that 

 all the shells of the reefs reach to such enormous 

 size as those we have hitherto mentioned, for a 

 rich harvest of species awaits the eager concholo- 

 gist who hunts for the smallest shells he can find 

 in the pools. Within the last few years a large 

 number of new species of small Molluscs have 

 been described from the coral seas, many of which 

 do not attain to a total length of more than ^ 

 of an inch when perfectly adult, so that the 

 range in size of this class of animals is very great 

 indeed. 



So much has been said about the Madrepores, , 

 the Im perforate Corals and the solitary Corals 

 of the reef, that the impression might be left that 

 all the Polyps of the Tropics differ from those of i 

 the Temperate regions in the fact that they form i 

 shells or skeletal structures. This is by no means 

 the case, for there are many species of true Sea- 

 anemones and other Polyps to be found on Coral- 

 reefs which make no shell at all, and others in i 

 which the body -wall is strengthened by numerous, 

 but very minute spicules or grains of lime which, 

 on the decomposition of the animal's body, fall 

 down into a shapeless powder or sand. 



True Sea-anemones are not very abundant on then 

 reefs of North Celebes, but many species have< 

 been found on the Barrier-reef of the Australian 

 coast, and among them specimens reaching the* 

 gigantic size of two feet in diameter the largest .j 

 size attained by single individuals of the class of. 



