SPINIFERITES IN FLINT. 9239 
discovered with a lens of moderate power, or even by the 
unassisted eye ; but all will amply repay a microscopical 
examination, and the minutest can only thus be detected. 
meLIGN. 77. 
A GROUP OF SPINIFERITES IN FLINT. 
( Seen by transmitted light. ) 
Fig. 1.—A thintranslucent chip of flint ; nat. 
2.—The same magnified, and viewed by transmitted light ; 
showing a group of five SPINIFERITES. 
3.—The same more highly magnified. 
4.—SPIN. RAMOSUS; one of the animalculites seen in Hess 
very highly magnified. 
5.—SPIn. REGINALDI; one of thesame group ; x 300 diameters. 
6.—A variety of S. RAMosUS; another of the same cluster of 
SPINIFERITES, 
SPINIFERITES (Xanthidiwm, Ehrenb.). Lign. 77.—I pro- 
pose to describe in this place those elegant and very minute 
bodies, that occur in great numbers in the chalk and flint, 
and which, on the authority of M. Ehrenberg, were regarded 
as identical with the siliceous frustules of the genus of fresh- 
water Desmidiz, named Xanthidium* (ante, p. 91.) Later 
and more correct observations have proved that the fossils 
* 
__ ~* Several recent species of Xanthidium are figured in Plate IV. of 
_ this volume. 
t 
by 
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