188 ME. H. HAMSHAW THOMAS AND MISS N. BANCROFT ON 



bordered by two fine liaear membranes, beyond which are the thickening patcbes some- 

 what hemispherical in shape, with a straight inner surface and rounded or pointed ends. 

 The inner surface of each appears to be carried on as a wall, a fact which is of some 

 importance in the interpretation of the structure. There are two crescentic subsidiary 

 cells. 



In their structm^e these stomata resemble the examples seen in Otozamites, especially 

 O. graphicus, and also in Taniopteris vittata {cf. PL 19. fig. 12). 



T^NiopTERis VITTATA, Brongn. 



The entire linear-lanceolate fronds with a strong petiole, central midrib, and dichoto- 

 mising nervation which are so common in the Yorkshire plant-beds were designated 

 Tceniopteris vittata by Erongniart and, as the name implies, regarded as fronds or 

 pinnae of a fern . Phillips in 1829 (p. 147) regarded it as allied to the recent Scolo 



pendrium^ but subsequent authors * have for the most part considered it to be allied to 

 Marat tiopsis and have placed it among the Marattiales. Another view was that it had 

 affinities with the modern genus Oleandra, since it possessed a petiole with a clean-cut 

 base, which suggested that it had become detached from its original stem or rhizome by 

 the formation of an absciss-layer f ; thus the generic name of Oleandridium was used by 

 Schimper [loc. cit.), Peistmantel, and others. 



On the other hand, the view was put forward by some authors, especially Bornemann 

 (1856, p. 59), that it was really the pinna of a pinnate Cycadean frond such as Stangeria, 

 and the name Stangerites was instituted to replace Tceniopferis. Several subse- 

 quent authors have kept in mind this possibility, but no definite evidence has been 

 forthcoming in support of either view, T. vittata has never been found bearing synangia 

 or sporangia ; it has also never been found attached as a pinna to a larger frond. 

 Recently, however, it has been found in association with Cycadean stems of the 

 Wielandiella type, and one specimen appears to show organic connection between a 

 frond and one of these stems. It is almost certain that we have to deal with entire 

 fronds and not with pinnae, and thus a very close comparison is ofPered with the 

 fronds of Anomozamites ( Wielandiella) ; the latter possess the forking nervation of 

 T(pniopteris and may be regarded as segmented fronds of the Tceniopteris type. 

 T. vittata itself is sometimes found with the lamina divided into irregular segments. 

 When we come to examine the cuticular structure we obtain very strong confirmation 

 of the Cycadean view. 



In its cuticular structure Twniopteris vittata approaches very closely to Anomozamites 

 NiUsoni. The upper epidermis is fairly strongly thickened and was composed of 

 squarish to hexagonal cells, with somewhat sinuous walls (PL 20. fig. 5). The vein- 

 courses are only slightly differentiated, the cells being more regularly arranged in rows. 

 The outline of the cell-walls is interesting owing to the presence of a solid piece of 

 thickening at the point of every fold (this is just visible in the photograph) ; in some 

 cases it gives the appearance of an almost straight wall ornamented with projecting 



• 



Schimper (1869), p. 607. t Seward (1900), p. 158. 



