Silurian Hexacoralla.—
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.—
The Middle Devonian beds of Australia are chiefly limestones, such as the Buchan limestone, Victoria; the Burdekin Series, Queensland; and the Tamworth limestone of New South Wales. These rocks, as a rule, are very fossiliferous, and the chief constituent fossils are the Rugose and Perforate Corals. Campophyllum gregorii is a common form in the Buchan limestone ([Fig. 70 A]), as well as some large mushroom-shaped Favosites, as F. gothlandica and F. multitabulata. Other genera which may be mentioned as common to the Australian Middle Devonian rocks are, Cyathophyllum, Sanidophyllum and Spongophyllum, Heliolites is also found in limestones of this age in New South Wales and Queensland.
Fig. 70—UPPER PALAEOZIC CORALS.
A—Campophyllum gregorii, Eth. fil. Mid. Devonian. Buchan, Vict.
B—Pachypora meridionalis, Nich. & Eth. fil. Mid Devonian. Queens.
C—Aulopora repens, Kn. & W. (after Hinde). Devonian. Kimberley district, W.A.
D—Zaphrentis culleni, Eth. fil. Carboniferous. New South Wales.
E—Trachypora wilkinsoni, Eth. fil. Carbopermian (Up. Marine Ser.) New South Wales.
F—Stenopora crinita, Lonsdale. Carbopermian (Up. Mar. Ser.) N.S.W.
In the Burdekin Series (Middle Devonian) in Queensland we also find Cystiphyllum, Favosites gothlandica, and Pachypora meridionalis ([Fig. 70 B]), whilst in beds of the same age at Rough Range in Western Australia are found Aulopora repens ([Fig. 70 C]), and another species of Pachypora, namely, P. tumida.