HYDROZOAN CORALS 153 



Stylaster. — The other genus of Stylasterina that is 

 very common is Stylaster. This coral forms profusely 

 branched flabellate colonies which sometimes attain to a 

 great size and when found in shallow water often possess 

 such a beautiful rose-pink colour that they are used for 

 ornamental purposes. The older branches of these Styl- 

 asters are very hard and are frequently mistaken for the 

 precious coral, but as they are perforated by the pores and 

 by the canal system they do not readily take a smooth polish 

 and are consequently of little value as jewels or charms. 



This coral can be distinguished from the precious coral by 

 two characters. In the first place, the branches are far more 

 numerous and terminate in very delicate twigs which may 

 be only 2 mm. in diameter. In the second place, there 

 can be found densely clustered on the terminal branches, and 

 more sparsely on the larger ones, a number of cyclo-systems. 



These pore-cycles in Stylaster are frequently raised on a 

 little prominence above the general surface of the corallum, 

 and when examined with a magnifying glass exhibit a 

 number of radially arranged ridges which have a striking 

 resemblance to the septa of a Madreporarian coral. When 

 the pore-cycles are prominent in this wa}^ they are usually 

 called " calices," although there is no true homology between 

 the calyx of a Stylaster and the calyx of a Madrepore (Fig. 72) . 



In each of these calices there is a centrally placed pore — 

 the gasteropore — and close to the margin a circle of ten or 

 more dactylopores. In each of these pores there is a short 

 tuberculated st\de which has a very rough resemblance to 

 a shaving brush. The ampullae can be seen as rough ex- 

 crescences between the calices in almost every specimen 

 that is examined. 



Stylaster is a genus with an extraordinarily wide geo- 

 graphical distribution. It is found in shallow water in most 

 of the tropical seas and in the deeper waters as far down as 

 900 fathoms. The deep-sea species are usually white, and 

 the calices are situated on one surface only of the flabellum. 



Allopora. — Closely related to Stylaster is the sub- 

 genus Allopora, which is found in the deep fjords of Norway 

 and British Columbia, and in 50 fathoms off the Cape of 



