Fig. 20—A Fossil Lobster (Thalassina emerii, Bell).
Slightly reduced. From the Pleistocene of Port Darwin, Northern Territory.
(Nat. Mus. Coll.)
Fig. 21—An Ammonite (Desmoceras flindersi, McCoy sp.)
Half nat. size. Showing complex sutures. L. Cretaceous: Marathon, Flinders River, Queensland.
(Nat. Mus. Coll.)
CRUSTACEA.—The outer crust, or exoskeleton, of these animals is often hard, being formed of a compound of carbonate and phosphate of lime on an organic, chitinous base. The earliest forms of this group were the trilobites, commencing in Cambrian times, and of which there is a good representative series in Australian rocks. Remains of crabs and lobsters are found in the various Cainozoic deposits in Australia ([Fig. 20]), and also in the Jurassic in other parts of the world.