Cainozoic Crinoids.—
Pentacrinus stellatus is a species founded on some deeply indented pentagonal stem-joints found in the Oamaru Series (Miocene) at Curiosity Shop, South Canterbury, New Zealand, and also occurring in the Chatham Islands. This species has been identified in the Aire Coastal beds in Victoria, of the same age. Another generic type, Antedon, the beautiful “Feather Star,” is frequently met with in Janjukian strata in Victoria and South Australia, as at Batesford and Mount Gambier, represented by the denuded crown and the ossicles of the arms of a comparatively large species; whilst another and smaller form has been described from beds of the same age from borings in the Victorian Mallee, under the name of A. protomacronema.
BLASTOIDEA—Bud-shaped Echinoderms.
Distribution and Characters of Blastoidea.—
This forms a small class which has a few representatives in the rocks of Australia. Elsewhere they are chiefly of Devonian and Carboniferous ages. In Australia they are confined, so far as known, to sediments of the Carboniferous System. The animal was rooted to the sea-floor and a jointed stem was usually present. The cup or theca, as before noted, is bud-shaped, and consists of basal, radial and deltoid plates, the edges of which are folded inwards into the thecal cavity, and thus the internal organs came into contact with the incurrent water. The cup bears five food grooves, bordered by numerous arms or brachioles, which directed the incurrent particles into the thecal cavity.
Carbopermian Blastoids.—
Three genera of blastoids have been recorded from the Gympie Beds, or Carbopermian, of the Rockhampton District of Queensland. They are, Mesoblastus, Granatocrinus and Tricoelocrinus. A similar fossil in beds of like age, and provisionally referred to the genus Metablastus, has been lately recorded from Glenwilliam, Clarence Town, New South Wales.
ASTEROIDEA, or Starfishes.
Characters of True Starfishes.—
These free-moving echinoderms are usually five-sided, though sometimes star-shaped, with numerous arms surrounding a central disc. The mouth is central on the under side of the disc, and the anus above and near the centre (excentric), the latter being covered by a porous plate called the madreporite. The hydraulic system of starfishes consists of tubes extending along the grooved arms and giving off side branches which end in processes called podia and terminating in suckers. The podia pass through pores in the floor plates of the grooves, and communicate within the body with distensions called ampulla. By this means the podia serve as feet, and can be withdrawn by the expulsion of the water in them into the ampulla. The stout flexible covering of the starfish is strengthened by calcareous plates and bars, owing to the presence of which they are often preserved as fossils.