INTRODUCTION. 193 
hood, also contains a good many Calcisponges, principally belonging to Holco- 
spongia floriceps, Phillips, sp., which frequently grows in colonies of considerable size. 
This same species, together with Holcospongia polita, Hinde, and Blastinia 
aspera, Hinde, is fairly abundant in the Lower Limestone belonging to the upper 
part of the Am. perarmatus-zone at Suffield and Hackness, near Scarborough. 
Calcisponges are also fairly common in the white limestones of the higher 
horizons of the Corallan Oolite and Coral Rag at Langton Wold, near Malton, 
and at Settrington; they belong to Corynella Langtonensis, Hinde; C. Chadwick, 
Hinde ; and Holcospongia glomerata, Quenst., sp. 
Though Calcisponges are abundant in the Corallian series of Yorkshire, they 
are rare in the corresponding beds in the South-west of England; only a few 
examples of Holcospongia are as yet known from the Coral Rag of Lyneham, 
Wiltshire. 
From the Portland beds no entire fossil sponges are as yet known, but in some 
of the chert nodules in the limestones on the Isle of Portland and at Upway, near 
Weymouth, there are numerous detached spicules of Pachastrella antiqua, Moore, 
sp., and of Geodites, sp., thus showing that, in part at least, the chert of these 
rocks is derived from sponge remains. 
In the fresh-water beds of the Purbeck series at Stare Cove, Dorsetshire, 
cherty nodules are present, and some of these were found by Mr. J. Young to be 
composed of minute acerate spicules which are referred to Spongilla Purbeckensis, 
Young. 
From the different divisions of the British Jurassic series, fifty-six species of 
fossil sponges are described in the following pages; of these, twenty species are 
Siliceous sponges and thirty-six Calcisponges. The following list shows the 
numbers in each group: 
Siliceous Sponges. Calcisponges. 
Lias 2 i] 
Inferior Oolite 15 19 
Great Oolite . — 14 
Corallian 1 7 
Portland Beds 2 — 
Purbeck Beds ih — 
Very few species pass from one division to another; of the siliceous sponges, 
only one, Pachastrella antiqua, Moore, sp., which occurs at the bottom of the Lias 
and again in the Portland beds. Four species of Calcisponges are present both in 
the Inferior Oolite and in the Great Oolite, and one species is common to the Great 
Oolite and the Corallian rocks. Hexactinellid sponges have only been found in 
the Inferior Oolite, and here they are accompanied by Lithistids and Calcisponges. 
Of the fifty-six species recognised in the British area, only nine occur in the 
