PLATE 19, 20. 
The above specimens exhibit the upper surface of the 
Irond. The nodules sometimes break, so as to show the 
under surface. In this case the petrifaction itself is con- 
cave, its Impression, in the other half of the nodule, convex ; 
contrary to what is generally observable in fossil leaves. 
FIG. 4, 5, 6. 
PHYTOLITHUS Plantites (slellatus) caule slm- 
plice tereti striato, foliis linearibus verticillatls. S. p. 
A fossil vegetable. Original a Plant. Stem simple, 
round, slightly striated in a longitudinal direction. Leaves 
whorled, linear, entire, about twelve or fourteen in each 
whorl. The whorls numerous, but distant. 
Found now and then in ironstone, coal, bind, &c. with 
other vegetable remains. 
The prototype of this petrifaction is generally supposed 
to be an Equisetum or Horsetail; but there are other plants 
with stellate leaves, to which it might with as much propri- 
ety be referred ; Hippuris, Asperula and Galium for instance. 
We may here observe^ that little has yet been done with 
respect to discriminating the original genera of fossil plants: 
those parts, indeed, .on which such discrimination must be 
founded, are rarely, if ever, visible in the petrified state. 
I 
