PLATE XXI
1. A transparent flat branch-with canals , but no perforations-as seen with half-inch objective : in slide . Chimborazo, No. 4.
2. A six- sided cushion, still a Stephanastrum.
3. Stylosphora of Ehrenberg ; rather dwarfed, and one spine become bifid .
4. Many-spined Haliomma?
5. A Polycystin, not unfrequent in Barbados earth.
6. A massive beautiful spine, looks as if it might have been the central support of some organism.
7. Again one of these Plate- spicules-of what ? Dr. Greville suggested , July, 1863 , that it might probably be Actiniscus Stella : professor Bailey considered Actiniscus as a Polycystin.
8. A fenestrated Pyramid, possibly a Podocyrtis ; similar to figs . 5 and 6 on plate 12 , but with this remarkable difference, that the bars , or net-work of Silex bounding the window- like openings, appear to be very finely perforated or cellulated. Dr. Wallich examined this specimen , and considered that the roughened, or apparently cellular
appearance, might have arisen from a diseased state of the sarcode while depositing the siliceous bars. I have noticed the same appearance on parts of other specimens, and on spines which. have become bulbous at the ends. No inner web discernible through these windows.
9. & 10. Beautiful little siliceous stars . Cambridge, Barbados.
11. An extraordinary Silicified cast of the septal lines and primordial segment with part of the interior of a Textilaria ; in a slide from Springfield, Barbados . Dr. Davy. That the original Carbonate is changed to Silex is proved, not only by its having resisted the treatment with strong acids and alkalis used in preparing the Barbados earths for the microscope, but also that no colour was shewn under the strong Polarizing apparatus of powerful microscopes ; and the process of such a change is perfectly explained by Professor Ehrenberg's account of the infiltration of silicate of iron into some of the Foraminifera, giving thus perfectly preserved casts of the inside of the shells * ; this specimen measures .0131 in length. * Note. " Ueber den Grünsand, und seine Erlauterung." Berlin, 1856.
