PLATE XXIV
1. A magnificent Spicule , probably of some unknown sponge; but as, on careful examination of the beautiful figures of Dr. Bowerbank and Professor Max Schultze (kindly lent by Dr. Gray) none appear identical, it is introduced here to exemplify
its approach in character to some of the Polycystin spines (or spicules) in slide 48 .
Chimborazo Barbados . Dr. Davy.
2. & 3. Polycystins, the whole of whose siliceous shells appear to be running out into spines, simulating, or asserting, their relationship to sponge- spicules. Barbados.
4. A broken spine of a Polycystin ? highly magnified, shewing the construction, and that the fine thorn-like " secondary spicules " are really points of support for , or commencements of, the siliceous net-work of the shell . Barbados slide, 102.
5. Three similar spines in situ , with their enveloping net-work, so far broken away as to shew the thorny spikes near their centre of junction with 1/2 inch . Barbados slide, 108.
6. Six long slender spines , proceeding from a radial axis, and becoming roughened with little thorny spines at about half-way from the centre, and then tapering to fine points . Barbados slide 108.
7. A variety of Stephanolithis Nodosa of Ehrenberg. Mikrogeologie ; Pl . XXXVI , figs . 57, 58. slide V. Cambridge, Barbados.
