PLATE XXIV. 

 no. 



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 Polycystip spines (or sjjicules) in 

 slide 48. Chimborazo, Barbados. Dr. Davy. 



2 & 3. — Polyeystins, the whole of whose siliceous shells appear to be 

 running out into spines, simulating, or asserting, their relation- 

 ship to sponge-spicules. Barbados. 



4. — A broken s])ine of a Polycystin ? highly magnified, shewing the 

 construction, and that the fine tliorn-like " secondary spicules " 

 are really points of support for, or commencements of, the sili- 

 ceous 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 half-inch. Barbados slide, 108. 



6. — Sis long slender spmes, 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 ; 

 PI. XXXVI, figs. 57, 58; slide V. Cambridge, Barbados. 



