Yol. 63.] OF THE INFEEIOR OOLITE OF BEOEA. 379 



characteristic of the Brora beds and have not (so far as I am 

 aware) been found elsewhere, they are described under the (perhaps 

 temporary) name of Equisetites broraensis. 



The Zamites-])mmiles, although differing from any described 

 species to which I have access and reference, are yet insufficiently 

 preserved to justify a new name for them. 



The Ginkgo-le&Yes are very much better preserved than the other 

 plants, and are of some interest. As is seen in PI. XXVII, figs. 

 3 & 4, they are of a deeply-bilobed type, and they may vary from 

 2 to 4 centimetres in expansion. They entirely correspond with 

 the type figured by Prof. Seward (00), p. 259 & pi. ix, fig. 10, 

 from the Yorkshire Oolites, as one of the varieties in the form of the 

 leaf of Ginkgo digitata. Among the Brora specimens this deeply- 

 bilobed variety is the common form, no other shape of leaf of the 

 species or of other species of Ginkgo or Baiera occurring, except 

 one or two small simple leaves without any lobing. One of these 

 is illustrated in PI. XXVII, fig. 5. Both the simple and the bilobed 

 variety can be matched among the smaller leaves of the living form 

 [see Seward & Gowan (00), where the great variability in shape of 

 the leaves is illustrated] ; hence, although Prof. Seward does not 

 illustrate the simple type in his series of Oolitic fossils (op. supra cit. 

 pi. ix), there appears to be no necessity to conclude that it is any- 

 thing but a variety of form of Ginkgo digitata, although at one time 

 it would have received specific distinction. 



"When the shales were freshly opened the leaves were extremely 

 liable to peel off nearly complete, and even to blow away, the leaf 

 separating intact from the shale and showing the veining very 

 clearly when held up to the light. Some of these leaves were 

 treated with nitric acid and potassium-perchlorate for several days 

 and then carefully washed, when it was found that not only had 

 they become perfectly transparent, but that it was possible to split 

 them horizontally and thus separate sheets of upper and lower 

 epidermis, each retaining the perfect form of the leaf. The details 

 of the epidermal cells were then perfectly recognizable under the 

 microscope, and in some of the better specimens the stomates and 

 guard-cells were perfectly preserved. There is a distinct difference in 

 character between the upper and the lower epidermis, as is shown in 

 the text-figure (A & B, p. 380), the stomates being almost entirely 

 confined to one side of the leaf, which is presumably the lower, 

 although one or two were observed on the other side as well. 



As the outlines of the cells were so perfectly preserved, it seemed 

 worth comparing them with the corresponding cells of the living 

 species. The result is shown in the text-figure, where A & C and 

 B & D correspond. All these figures were drawn with the same lens 

 and eyepiece, with a ' Netzmikrometer/ on mathematical paper, 

 so that they are on an identical scale. It will be evident that the 

 difference in form between the cells of the living and the fossil 

 species is entirely sufficient to justify specific distinction. Judging 

 simply by the external form of the leaves, it is not possible to deter- 

 mine whether the Jurassic G. digitata is or is not a different species 



