It is, however, to the next group, the Hexacoralla, with septa in multiples of six, twelve, and twenty-four, that we turn for the most varied and abundant types of Corals in Silurian times. The genus _Favosites_ (Honey-comb Coral) is extremely abundant in Australian limestones (Fig. 69 B, C), such as those of Lilydale, Walhalla, and Waratah Bay in Victoria, and of Hatton's Corner and other localities near Yass, in New South Wales. _Pleurodictyum_ is also a familiar type in the Australian Silurian, being one of the commonest corals in the Yeringian stage; although, strange to say, in Germany and N. America, it is typical of Devonian strata (Fig. 69 E). _Pleurodictyum_ had a curious habit of growing, barnacle fashion, on the side of the column of the crinoids or sea-lilies which flourished in those times. _Syringopora_, with its funnel-shaped tabulae or floor partitions, is typical of many Australian limestones, as those from Lilydale, Victoria, and the Delegate River, New South Wales. _Halysites_ (Chain Coral), with its neat strings of tubular and tabulated corallites joined together by their edges, is another striking Coral of the Silurian period (Fig. 69 F). This and the earlier mentioned _Syringopora_, is by some authors regarded as belonging to the Alcyonarian Corals (typically with eight tentacles). _Halysites_ is known from the limestones of the Mitta Mitta River, N.E. Gippsland, Victoria; from the Molong and Canobolas districts in New South Wales; from the Gordon River limestone in Tasmania; and from Chillagoe in Queensland. Abroad it is a well known type of Coral in the Wenlockian of Gotland in Scandinavia, and Shropshire in England, as well as in the Niagara Limestone of the United States. =Silurian Octocoralla.--= Perhaps the most important of the Octocoralla is _Heliolites_ ("Sunstone"), which is closely allied to the Blue Coral, _Heliopora_, a frequent constituent of our modern coral reefs. The genus _Heliolites_ has a massive, calcareous corallum, bearing two kinds of pores or tubes, large (autopores) containing complete polyps, and small (siphonopores) containing the coenosarc or flesh of the colony. Both kinds of tubes are closely divided by tabulae, whilst the former are septate. _Heliolites_ is of frequent occurrence in the Silurian limestones of New South Wales and Victoria (Fig. 69 G). =Devonian Corals.--=