The sub-kingdom of ECHINODERMATA includes the above groups comprised in the Classes Crinoidea, Asteroidea, Ophiuroidea and Echinoidea. Besides these are the less important classes of the Cystidea or sac-shaped echinoderms (of which no definite remains are recorded from Australian rocks); the Blastoidea or bud-shaped echinoderms (of which four genera are known from Australia); the Edrioasteroidea or sessile starfishes (unknown in Australia); and the Holothuroidea or sea-cucumbers (represented as fossils by the skin spicules and plates, an example of which has been recorded from Australia). _CRINOIDEA, or Sea-lilies._ =Crinoidea, their General Structure.--= These often beautiful and graceful animals resemble a starfish mounted on a stalk. They are composed of calcareous joints and plates, and are therefore important as rock-formers. The stalk or column may be either short or long, and is generally rooted, in the adult stage, in the mud of the sea-floor. Fossil Crinoids were sometimes furnished with a coiled termination, which could be entwined around such objects as the stems of sea-weeds. The crinoid column is composed of numerous plates, and is round or pentagonal. Upon this is fixed the calyx or cup, with its attached arms, which serve to bring food to the mouth, situated on the upper part of the cup. The arms are grooved, and the water, being charged with food particles (animalcula), pours down these channels into the mouth. The stem elevates the animal above the mud or silt of the sea-floor, thus making it more easy for it to obtain its food supply. The stalks of fossil Crinoids sometimes reached the enormous length of 50 feet. Their calcareous skeleton is built upon a plan having five planes of symmetry; this pentamerism is found throughout the crinoids, the blastoids and the free-moving echinoderma. Crinoids range from moderately shallow- to deep-water, and at the present day are almost restricted to abyssal conditions. The more ancient types usually found their habitats amongst reefs or in comparatively clear water, where there was a marked freedom from sediment, although that was not an essential, as seen by their numerous remains in the Australian mudstones and sandstones. =Cambrian Crinoids.--= The group of the Crinoidea first appears in the Upper Cambrian, and persists to the present time. In North America the genus _Dendrocrinus_ occurs in the Cambrian and Ordovician; and some stem-joints from the Upper Cambrian limestone of the Mount Wellington district, Victoria, may be provisionally referred to this genus. [Illustration: =Fig. 76.--FOSSIL CRINOIDS.= A--(?) Pisocrinus yassensis, Eth. fil. Side of calyx. Silurian. Yass, New South Wales. B--(?) Pisocrinus yassensis, Eth. fil. Dorsal Surface. Silurian. N. S. W. C--Botryocrinus longibrachiatus, Chapm. Silurian. Flemington, Vict. D--Helicocrinus plumosus, Chapm. Stem, distal end. Brunswick, Victoria.