ii8 CORALS 



distribution, however, is that the same species occurs in 

 deep water in the fjords of British ("ohunbia and a closely 

 allied species off the coast of Japan. 



So far as our knowledge of its distribution goes, there- 

 fore, it seems to be a species confined to the cold deep 

 waters of the Northern Hemispheres with two remarkable 

 breaks in its continuity, one in the North Atlantic and the 

 other the American continent. It affords, therefore, an 

 interesting problem for students of geographical distribution. 



Heliopora. — It was formerly supposed that Heliopora 

 was a Zoantharian coral until Moseley, during the voyage of 

 the Challenger Expedition, examined the polyps of some 

 specimens at Samboangan and proved that they have all 

 the essential characters of the Alcyonaria. But although 

 it is an Alcyonarian it occupies a unique and isolated 

 position in that Order on account of its massive corallum 

 of crystalline calcium carbonate, by the absence of the 

 characteristic Alcyonarian spicules, and by other structural 

 peculiarities. 



There is one character which distinguishes the corallum of 

 Heliopora from all others, and that is the blue colour which 

 gives it its specific name. There is no other coral belonging 

 to any group that possesses this colour, and in every specimen 

 of Heliopora that has been examined the colour either per- 

 meates the whole corallum or can be seen just below the 

 surface in a fractured branch. On this account it has 

 received the popular name of " The Blue coral." 



The form of the colony is very variable. It may be 

 branched like a stag's horn Madrepore, laminate, or almost 

 massive, but the ends of the branches are usually blunt and 

 lobed. It sometimes reaches a size of three or four feet in 

 diameter by two feet or more in height. 



The surface of the corallum is rough and is perforated 

 by two kinds of pores, which may be called the large pores 

 and the small pores respectively, the small pores being very 

 much more numerous than the large ones. On looking 

 down into a large pore with a magnifying glass, a variable 

 number of shallow ridges may be seen projecting into the 

 lumen, which have a certain resemblance to the septa of 



