ABSTRACT
Fossil sponges take an important place among the organic remains of the former world, not only on account of their great variety of form and structure, but more because of the extraordinary abundance of individuals in certain strata. The calcareous sponges abound in the oolitic and cretaceous strata, attaining their maximum of development in the chalk; they are almost extinct, or are represented by other families with calcareous spicula. Palaeospongia and Acanthospongia occur in the lower Silurian; and Stromatopora, with its concentrically laminated masses, attains a large size in the Wenlock limestone. Steganodictyum, Sparsispongia, and species of Scyphia, are found in the Devonian; and Bothroconis, Mamillopora, and Tragos, in the Permian or magnesian limestone. Several genera are common to the trias and oolites, and several more are peculiar to the latter strata. The sponges, chiefly Siphoniae, of the upper greensand of Farnham are infiltrated with phosphate of lime, and have been used in agriculture.
