Thinnfeldia Leaf-Bed of Roseberry Topping. II 
Hungary. Though Dr. Gothan has questioned this deter- 
mination on the ground of the stomatal structure, it is 
supported by the shape of the fronds and pinnae, and by 
the nervation. The species also occurs on the continent, in 
the Rhaetic of Franconia (Bayreuth), and in France ;— while 
it may perhaps be identical with some forms occurring in 
India and South America. In England the type first became 
known from specimens found in the Lias at Lyme Regis, but 
more recently it has been described from the Kimeridgian beds 
of Sutherlandshire by Prof. Seward. Hitherto the genus has 
not been definitely recorded from any of the other plant beds 
in Yorkshire and is certainly entirely absent from all the coast 
localities. I have seen a single specimen in the collection of 
Mr. Sewell, of Whitby, which was badly preserved but was 
probably referable to the genus, it came from one of the inland 
localities in the neighbourhood of Goathland. While we are 
probably correct in saying that Thinnfeldia is more typical 
of the Lias than of the Middle Jurassic, we must remember that 
the Sutherland specimens are of Kimeridge age and that 
somewhat similar fronds have been described from the Wealden 
beds under other generic names, such as Dichopteris. 
We may now turn for a moment to discuss the nature and 
affinities of these leaves. 
As in the case of so many other fossil plants, the leaves of 
Thinnfeldia have always been found in an isolated condition 
and never connected with any reproductive structures. Under 
these conditions we have only two things on which to base our 
conclusions and both of them are somewhat untrustworthy. 
The first is the form and nervation of the leaf, the second the 
epidermal structure. Early observers basing their conclusions 
on the first named character thought, that Thinnfeldia was a 
fern, for the outlines, and the nervation were quite fern- 
like. Against this view there are two objections (@) that 
no leaf bearing sporangia has ever been found, and in the 
millions of leaves at Roseberry some at least should be present. 
and (b) that the texture of the leaf, and the cuticle must have 
been very different from that seen in the ferns of to-day. 
This brings us to the study of the cuticle, and for this 
microscope preparations of the epidermal structures must 
be made. This is effected by placing part of a pinna in a 
watch glass or a small porcelain dish, covering it with small 
crystals of potassium chlorate, and adding a few cubic centi- 
metres of strong nitricacid. The dish is covered up and allowed 
to stand for a day or two until the leaf fragment has assumed 
a brown colour; the fragment is then removed, washed in 
water and placed in a very dilute solution of ammonia, when the 
brown material soon dissolves away, leaving a clear semi- 
transparent and very fragile membrane. This consists of the 
1915 Jan. 1. 
