Subdivisions.—
Radiolaria are divided into the four legions or orders,—Acantharia, Spumellaria, Nasselaria and Phaeodaria: only the second and third groups are found fossil. The Spumellarians are spherical, ellipsoidal, or disc-shaped, and the Nasselarians conical or helmet-shaped.
Cambrian Radiolaria.—
Certain cherts or hard, siliceous rocks of the palaeozoic era are often crowded with the remains of Radiolaria, giving the rock a spotted appearance. (See antea, Fig. 38). Some of the genera thus found are identical with those living at the present day, whilst others are peculiar to those old sediments. In Australia, remains of their siliceous shells have been found in cherts of Lower Cambrian age near Adelaide. These have been provisionally referred to the genera Carposphaera and Cenellipsis ([Fig. 66]).
Ordovician Radiolaria.—
Radiolaria have been detected in the Lower Ordovician rocks of Victoria, in beds associated with the Graptolite slates of this series. In New South Wales Radiolarian remains are found in the cherts and slates of Upper Ordovician age at Cooma and Mandurama.
Silurian Radiolaria.—
The Silurian black cherts of the Jenolan Caves in New South Wales contain casts of Radiolaria.
Devonian Radiolaria.—
The Lower Devonian red jaspers of Bingera and Barraba in New South Wales have afforded some casts of Radiolaria, resembling Carposphaera and Cenosphaera.