Polyzoa are divided into the Sub-classes Phylactolaemata, in which the mouth of the zoöid has a lip, and the series of tentacles is horse-shoe shaped; and the Gymnolaemata, in which there is no lip to the mouth, and the tentacles form a complete circle. The first group forms its polypary of soft or horny material, which is not preserved fossil. The latter has a calcareous polypary, and is of much importance as a fossil group. This latter sub-class is further subdivided into the following Orders, viz.:--Trepostomata ("turned mouths"), Cryptostomata ("hidden mouths"), Cyclostomata ("round mouths"), and Cheilostomata ("lip mouths" furnished with a moveable operculum). =Trepostomata (Palaeozoic).--= The Order Trepostomata may include some genera as _Monticulipora_ and _Fistulipora_, previously referred to under the corals. They become extinct after Permian times. _Fistulipora_ occurs in certain Gippsland limestones. [Illustration: =Fig. 83--PALAEOZOIC POLYZOA.= A--Fenestella margaritifera, Chapm. Silurian. Near Yering, Vict. B--Polypora australis, Hinde. Carbopermian. Gascoyne River, Western Australia C--Rhombopora tenuis, Hinde. Carbopermian. Gascoyne River, Western Australia D--Protoretepora ampla, Lonsdale sp. Carbopermian. N.S.W. ] =Cryptostomata (Palaeozoic).--= In the order Cryptostomata we have the genus _Rhombopora_ with its long, slender branches, which occurs in the Silurian of Victoria and the Carbopermian of Queensland and W. Australia (Fig. 83 C). Of this order a very important Australian genus is _Fenestella_, the funnel-shaped zoaria of which are found in the Silurian of Victoria and New South Wales, and also in the Carboniferous of the latter State. _Fenestella_ also occurs in the Carbopermian of W. Australia and Tasmania (Fig. 83 A). Accompanying the remains of _Fenestella_ in the Carbopermian rocks, and closely related to it, are found the genera _Protoretepora_ and _Polypora_ (Fig. 83 B, D). Polyzoa have been noticed in Jurassic rocks in W. Australia, but no species have been described. [Illustration: =Fig. 84--CAINOZOIC POLYZOA.= A--Lichenopora australis, MacGillivray. Balcombian. Hamilton, Victoria B--Heteropora pisiformis, MacGillivray. Janjukian. Moorabool, Victoria C--Cellaria australis, MacGillivray. Balcombian. Hamilton, Vict. D--Selenaria cupola, T. Woods sp. Balcombian. Hamilton, Vict. E--Lepralia elongata, MacGill. Balcombian. Hamilton, Victoria ] =Cheilostomata (Cretaceous).--= Species of the genera (?) _Membranipora_ and (?) _Lepralia_, belonging to the Cheilostomata, have been described from the Lower Cretaceous of the Darling River, New South Wales, and Wollumbilla, Queensland, respectively. =Cainozoic Polyzoa.--=