664 PROFESSOR A. C. SEWARD ON 



Gleichenites cycadina (Schenk). (Text-fig. 5 ; PI. III. figs. 48-54A ; 



PL V. figs. 87-89, 92-96.) 



1871. Alethopteru cycadina, Schenk, Palxontographica, Bd. xix. p. 218, pi. xxvii. figs. 6, 6a> 



pi. xxxi. fig. 2. 

 1871. Pecopteris Dunlceri (pars), ibid., pi. xxxi. fig. 1. 

 1876. Alethopteris cycadina, Schenk, Palzont., Bd. xxiii., pi. xxvi. fig. 6. 



1894. Nathorstia valdensis, Seward, Wealdm Flora, vol. i. p. 145, pi. vii. fig. 5, pi. ix. figs. 2, 2a. 



1895. Leckenbya raldensis, Seward, Wealden Flora, vol. ii. p. 225. 



1900. Leckenbya valdensis and Cladophlebis Dunkeri (pars), Seward, Mem. Mus. d'Hist. Nat. 

 Belgique, tome i. p. 24, pi. iii. figs. 42-46, 51. 



The fern identified as Gleichenites cycadina is one of the commonest species in the 

 Culgower flora, but its abundance is no doubt in great measure due to the delicate or 

 brittle structure of the pinnae ; it occurs almost always as very small pieces of fronds. 

 The best specimen is that represented in fig. 50, PL III., one of the few examples 

 showing pinnae in connection with a supporting axis. The examination of a large 

 number of examples enables me to give the following incomplete diagnosis : — Frond 

 compound; pinnse, which are given off at a wide angle (fig. 50), usually narrow and 

 linear, and probably reaching a considerable length without much difference in breadth ; 

 as seen in figs. 52, PL III., 88, 89, PL V., they taper very gradually towards the 

 distal end. The fronds also bore pinnae of a lanceolate form with pinnule decreasing 

 more rapidly in length towards the apex of the pinna (figs. 54, PL III. ; 94, 95, 

 PL V.). Pinnules thick, contiguous or-slightly separated (figs. 48, 49, 52, PL III. ; text- 

 fig. 5, A, B), varying considerably in size and form ; the smaller pinnules may be more 

 or less semicircular, sub-orbicular, or deltoid (cf. figs. 51, 5lA, 53, PL III. ; 87, 89, 

 PL V.), with a bluntly rounded apex and basal angles; these pass into longer and 

 relatively narrower segments (figs. 48, 48A, 50. 52, etc.), some of which are several 

 times longer than broad (e.g. fig. 49, PL III.). In the case of some of the smaller 

 pinnules the lamina appears to be attached by the whole breadth of the base (figs. 92, 96), 

 but in this specimen the actual pinnules are not preserved and the appearance of the 

 hollow mould may be misleading. As a rule the base of the pinnule is rounded and 

 the lower edge forms a prominent and thick lobe (figs. 48A, 49, PL III. ; 87, 88A, 

 PL V.). In the unusually large pinnule represented in fig. 92, PL V., the upper edge of 

 the base is slightly lobed. The lamina is usually entire, but in the longer pinnules the 

 edge becomes crenulate (figs. 54, 54A, PL III. ; 93, 93A, 95, 95A, PL V.). The sori 

 are circular and occur in a single row on each side of the midrib ; they are best seen in 

 pmnules from which the thick carbonaceous film has been removed, and are preserved as 

 a projecting circular rim enclosing a depression which no doubt marks the position of a 

 central receptacle like that in Laccopteris and other ferns (figs. 54A, PL III. ; 95A, PL V.). 

 No sporangia have been found. The venation consists of a midrib giving off dichoto- 

 mously branched veins at a fairly wide angle (figs. 48 A, 49, PL III. ; 87, 96, PL V. ; 

 text-fig. 5). The thick carbonaceous layer representing the lamina indicates pinnules 

 of a fleshy xerophilous type. 



