The _FORAMINIFERA_ are a group which, although essentially one-celled, have the protoplasmic body often numerously segmented. The shell or test formed upon, and enclosing the jelly-like sarcode, may consist either of carbonate of lime, cemented sand-grains, or a sub-calcareous or chitinous (horny) covering. The Foraminifera, with very few exceptions, as _Mikrogromia_, _Lieberkuehnia_, and some forms of _Gromia_, are all marine in habit. Some genera, however, as _Miliolina_, _Rotalia_ and _Nonionina_, affect brackish water conditions. Since Foraminifera are of so lowly a grade in the animal kingdom, we may naturally expect to find their remains in the oldest known rocks that show any evidence of life. They are, indeed, first seen in rocks of Cambrian age, although they have not yet been detected there in Australian strata. =Cambrian Foraminifera.--= In parts of Siberia and in the Baltic Provinces, both Cambrian and Ordovician rocks contain numerous glauconite casts of Foraminifera, generally of the _Globigerina_ type of shell. In England some Middle Cambrian rocks of Shropshire are filled with tiny exquisitely preserved spiral shells belonging to the genus _Spirillina_, in which all the characters of the test are seen as clearly as in the specimens picked out of shore-sand at the present day. =Silurian Foraminifera.--= The Silurian rocks in all countries are very poor in foraminiferal shells, only occasional examples being found. In rocks of this age at Lilydale, Victoria, the genus _Ammodiscus_, with fine sandy, coiled tests, is found in the Cave Hill Limestone. So far as known, hardly any forms of this group occur in Devonian strata, although some ill-defined shells have been found in the Eifel, Germany. =Carboniferous Foraminifera.--= The Carboniferous rocks in many parts of the world yield an abundant foraminiferal fauna. Such, for instance, are the _Saccammina_ and _Endothyra_ Limestones of the North of England and the North of Ireland. The Australian rocks of this age have not afforded any examples of the group, since they are mainly of estuarine or freshwater origin. [Illustration: =Fig. 63.--PALAEOZOIC and MESOZOIC FORAMINIFERA.= A--Nubecularia stephensi, Howchin. Carbopermian. N.S.W. B--Frondicularia woodwardi, Howchin. Carbopermian. N.S.W. C--Geinitzina triangularis, Chapman and Howchin. Carbopermian. N.S.W. D--Valvulina plicata, Brady. Carbopermian. West Australia. E--Vaginulina intumescens, Reuss. Jurassic. West Australia. F--Flabellina dilatata, Wisniowski. Jurassic. West Australia. G--Marginulina solida, Terquem. Jurassic. West Australia. H--Frondicularia gaultina, Reuss. Cretaceous. West Australia. ] =Carbopermian Foraminifera.--=