NATHORSTIA. 145 
Genus NATHORSTIA, gen. nov. 
I propose to institute a new provisional genus of ferns for 
the reception of certain specimens from the English Wealden, 
which do not conform to the definitions of any known fossil 
genera; and, as some slight testimony to the palwobotanical 
labours of Dr. Nathorst, I have ventured to name the plants 
after him. 
It will be seen that the specimens included under this genus 
are imperfectly preserved frond fragments, and of such a kind 
that it is impossible to arrive at any very satisfactory conclusion 
as to their real nature. 
Two of the pieces are shown in Pl. VII. Fig. 5 and Pl. IX. 
Fig. 2; these at first sight suggest portions of distinct species, 
and at first I regarded them as such. 
On more careful examination, however, and after comparison 
with other specimens, the differences become less pronounced and 
seem to be rather apparent than real. 
In the absence of venation and fructification it is useless to 
attempt a formal diagnosis of the genus; the characters will be 
most conveniently indicated in the definition of the single species. 
Nathorstia valdensis, gen. et sp. nov. 
1871. ? Pecopteris Geinitzii, Schenk (in part), Paleontographica, vol. xix. 
p. 215, pl. xxix. figs. 2 and 2a. 
Type. Portions of sterile fronds. British Museum. Pl. VII. 
Fig. 5.; Pl. IX. Figs. 2 and 2a. 
Frond bipinnate (?), of slender habit, rachis thin but well 
marked; pinne alternate or subopposite, long and of uniform 
breadth; the small pinnules attached by the whole of the base, 
margin entire or very slightly lobed, subdeltoid in shape, apex 
obtuse; some of the pinnules show faint traces of a midrib, but 
no lateral veins. Fructification unknown. 
The specimen figured by Schenk from the neighbourhood of 
Hannover as Pecopteris Geinitzii, Dunk., can hardly be referred 
to that species as figured by Dunker.'| On the whole it seems 
1 Wealdenbildung, pl. vii. fig. 3. 
