58 THE VOYAGE OF H.M.S. CHALLENGER. 



The pores are arranged in regular symmetrical eyclo-systems, a circular group of 

 dactylopores surrounding in each system a single centrally-placed gastropore. The pores 

 of both kinds occur only arranged in these systems in this species. 1 The cyclo-systems 

 so closely simulate in appearance the calicles of ordinary Hexactinian corals, that the 

 genus Stylaster and its allies, such as Allopora and CryptoheUa, have hitherto been 

 placed amongst the Oculinidae. The cyclo-systems in the present species appear as small 

 cylindrical masses of calcareous matter, which have a somewhat greater diameter at the 

 free extremity than at the base. In the growth of the coral new systems bud off from 

 the sides of the older cylinders, at the tips of the branchlets. The cylinders thus newly 

 formed have their axes at right angles to those of the old systems to which these are 

 attached, but in the same plane with them, which is also that of the entire flabellum. 

 The branchlets of the coenosteum, already described as given off by the main stem and 

 branches, are composed of zooid systems thus related to one another. In the more 

 recently formed twigs the arrangement described is plainly apparent, and they have thus 

 a zigzag appearance ; but in proportion as the branchlets are traced nearer and nearer to 

 the stems from which they spring, this zigzag arrangement becomes more and more 

 obliterated by deposit of ccenenchym, and in the older regions of the coenosteum, on the 

 sides of the main branches and stem, the mouths only of the zooid systems remain 

 unburied by the swollen dimensions of the support. 



No pore systems occur on either of -the flabellar faces of the stem or branches. Short 

 branchlets, as well as single pore systems, are evidently swallowed up, to some extent, 

 by the spread of ccenenchym and increase of the dimensions of the stem, and all 

 stages of the process appear at the lateral margins of the stem near its base. 

 But in order to secure an excessive strengthening of the stem, with the least amount 

 of encroachment upon early-formed pore systems, the stem swells to the greater 

 extent in the direction of its surfaces which correspond with the faces of the flabellum 

 and bear no pore systems. Hence, as already described, it becomes oval in section, 

 being flattened in a plane at tight angles to that in which the younger branchlets are 

 compressed. 



The cyclo-systems are groups of zooid pores as already described, which have a 

 regular symmetrical arrangement, a single gastropore in each system being surrounded 

 by a circlet of dactylopores. The centrally placed gastropore in each system is a wide 

 tubular cavity with a circular transverse section. This pore is much deeper than its 

 surrounding dactylopores, and has at its bottom a short stout style, with a brush-like 



1 In another species of Stylaster, S. granulata, dredged off Ascension Island, in 420 fathoms, small isolated dactylo- 

 pores were ohserved to occur on the surface of the coenosteum as a rare exception, apart from the pore systems. One 

 sucb was observed situate on the side of a cylindrical cyclo-system, and two others at the margin of an ampullar 

 prominence. These were very probably occupied, in the recent state of the coral, by small dactylozooids, the rudi- 

 ments of those which, in an earlier stage of evolution of the Stylasterida), overspread the surface of the ancestral form, 

 as in Sporadopora. 



