192 MR. H. HAMSHAAV THOMAS AND MISS N. BANCEOPT ON 



the cells very clearly. The cuticles of iV. mediana differ from those of N. compta on]y 

 in detail. The cells of the upper epidermis are more elongated and spindle-shaped, and 

 those of the lower epidermis are very sharply differentiated according to their position 

 above or between the nerve-courses (PI. 20. fig. 10). Some papillse are present, and each 

 of the rounded cells from the areas between the nerves is thickened externally and forms 

 in consequence a sliglit convex projection on the surface of the cuticle. The stomata 

 can be more clearly seen than in N. compta. The cells surrounding the stomatal 

 aperture are only slightly raised and thickened, and therefore they are less crushed. 

 The raised portions are in this species seen to be merely small outgrowths from the 

 ordinary epidermal cells, slightly thickened {cf, PI. 19. fig. 15). 



KiLSSONIA sp. 



A new form of Nilssonia has recently been discovered at Roseberry Toj)ping, Yorkshire. 

 It is closely allied to W, compta of the Middle Estuarine beds, but has more rounded and 

 less regular leaf- segments, approaching the N. polymorpha type. It also has a very 

 marked wrinkling of the lamina. It yields good cuticular preparations (PL 20. fig. 9), 

 though these are somewhat brittle. The stomatal apertures in this species are sur- 

 rounded by several strongly thickened conical cells which originally must have formed 

 conspicuous projections, but which are now usually much crushed (see PI. 19. fig. 13). 

 The papillate hairs are also well marked in this new form. 



Nilssonia orientalis, Heer. 



Of the three species of Nilssonia described in Prof. Seward's 'Jurassic Flora of 

 Yorkshire/ N. compta and N, mediana were well defined and represented by many 

 specimens in the then existing collections, while the third was only known from a few 

 examples. The name given to this was N. tenuinervis, a title which had originally been 

 proposed by Nathorst (1880. p. 35) for linear fronds, Kttle divided and having numerous 

 fine veins. It now seems impossible to separate this English form from the Siberian 



type described by Heer (1878, PI. 4. figs. 4-9) as N, 



In his original MS 



notes on the specimens amongst which iV. tenuinervis was found, Prof. Nathorst f 

 remarked on the great similarity in external form between the new species and some 

 examples of Tcenioptens mttata ; and, in fact, they can only be distinguished readily in 



well-preserved examples. In 1909, when working at the revision of the Swedish species 

 of Mls807iia and studying their epidermal characters, Prof. Nathorst (1909, p. 27) 

 made cuticular preparations of some fronds from Cioughton Wyke, Yorkshire, which 

 were in his collection. These preparations showed a type of structure unlike that of 

 the other MIssonias, and identical with that described above for Tceniopteris vittata. 

 Nathorst concluded that the Yorkshire frond was not a true Nilssonia, but was rather 

 allied to the ferns ; he accordingly instituted the new genus Nilssoniopteris, giving as 



« 



With 



Our I 



for showing me many of his manuscript notes and adding materially to the elucidation of this difficult 

 species. — H. H. T. 



