PLATE XXI. 



FIG. 



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 Stephauastrum. 



3. — Stylosphoera of Ehrenberg; rather dwarfed, and one spiue 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. GreviUe sug- 

 gested, July, 1863, that it might probably be Actiniscus stella; 

 Professor Bailey considered Actiniscus as a Polycystin. 



8. — A fenestrated Pyramid, possibly a Podocyi'tis ; similar to figs. 5 

 and 6 on plate 12, but with this remarkable difference, that the 

 bars, or network 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. 



1 1. — An extraordinary silicified east of the septal lines and primordial 

 segment, with part of the interior of a Textilaria ; in a slide from 

 Springfield, Barbados. Dr. Da\-y. 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 lor the microscope, but also that no colour 

 was shewn vmder the strong Polarizing apparatus of po^^•eJ■ful 

 microscopes ; and the process of such a change is perfectly ex- 

 plamed by Professor Ehrenberg's account of the infiltration of 

 siUcate of iron into some of the Foraminifera, gi\ing thus per- 

 fectly preserved casts of the inside of the shells*; this specimen 

 measures .0131 iu length. 



*Note. "Ueber don Grun.sand, uiid seine; Erlautcrung." Berlin, 18-56. 



