=Cainozoic Ostracoda.--= The fossiliferous clays and calcareous sands of the southern Australian Cainozoic beds often contain abundant remains of ostracoda. The moderately shallow seas in which the fossiliferous clays, such as those of Balcombe's Bay, were laid down, teemed with these minute bivalved Crustacea. All the forms found in these beds are microscopic. They either belong to living species, or to species closely allied to existing forms. Some of the more prominent of the Balcombian species are _Cythere senticosa_, a form which is now found living at Tenedos, and _C. clavigera_ (Fig. 114 B), with the young form sometimes referred to as _C. militaris_, a species which may still be dredged alive in Hobson's Bay. Other genera common in these clays are _Bairdia_, with its broad, pear-shaped carapace, represented by the still living _B. amygdaloides_ (Fig. 114 A). _Cytherella_, with its compressed, subquadrate carapace, as seen in _C. punctata_ (Fig. 114 D), a species having an elaborate series of muscle-spots, and which, like the previous species, is found living in Australian seas; and _Macrocypris_, with its slender, pointed, pear-shaped outline. =Cirripedia: Their Habits and Structure.--= _CIRRIPEDIA OR BARNACLES._--These curious modifications of the higher group of Crustacea (Eucrustacea) date back to Ordovician times. They appear to have tried every possible condition of existence; and although they are mostly of shallow water habits, some are found at the great depth of 2,000 fathoms (over two miles). Those which secrete lime or have calcareous shells, attach themselves to stones, pieces of wood, shell-fish, crabs, corals and sea-weeds. Others are found embedded in the thick skin of whales and dolphins, or in cavities which they have bored in corals or shells of molluscs. Some are found parasitic in the stomachs of crabs and lobsters, or within other cirripedes. They begin life, after escaping from the egg, as a free-swimming, unsegmented larva ("nauplius" stage), and before settling down, pass through the free-swimming, segmented "cypris" stage, which represents the pupa condition, and in which state they explore their surroundings in search of a suitable resting place for their final change and fixed condition. Just before this occurs, glands are developed in the pupa barnacle, which open into the suckers of the first pair of appendages or antennae. When a suitable place for fixation has been found, these glands pour out a secretion which is not dissolved by water, and thus the barnacle is fixed head downwards to its permanent position. The compound eyes of the "cypris" stage disappear, and henceforth the barnacle is blind. The characteristic plates covering the barnacle are now developed, and the six pairs of swimming feet become the cirri or plumes, with which the barnacle, by incessant waving, procures its food. In short, as remarked by one authority, it is