20 CYCADACE^;. 



as the presence or absence of a midrib. Schenk has pointed out 

 Bunker's error with regard to the supposed Wealden species of 

 Cycadites, C. Jforrisianus, Dunk., and a careful examination of the 

 English material confirms Schenk's correction. In some recent 

 species of Cycas the midrib is by no means obvious on the upper 

 surface of the pinnae ; e.g. iu a dried specimen of Cycas Cairnsiana 

 (Muell.), the upper convex surface of a pinna presents an appear- 

 ance suggestive of a few parallel veins, no doubt due to wrinkling, 

 rather than of a single midrib. In C. Jieddomei, Dyer, 1 the 

 margins of the pinna? are strongly revolute, and a cast of the 

 lower surface of a pinna would show too longitudinal ridges 

 separated by a distinct groove, the latter being formed by the 

 projecting central vein. On the other hand, the tendency to 

 a revolute margin in the long, narrow, linear pinna? of other 

 genera than Cycas, often leads to an appearance which might 

 easily be mistaken for a stout midrib in fossil specimens of such 

 a leaf. The under surface of the pinna? of Enceplialartos 

 Ghellinckii, Lern. (PL XIII. Fig. 3), Zamia angustifolia, Jacq., etc., 

 shows a narrow median groove separating the revolute edges of the 

 narrow segments, and this same folding might readily give rise to 

 a midrib-like character in the segments of fossil fronds. In a few 

 exceptional cases there is an anastomosis of the veins in cycadean 

 leaves; among fossil fronds Lindley and Hutton established the 

 genus C tents, for " all leaves having the general character of 

 Cycadefe, but with veins connected by forks or transverse bars." 

 As regards living genera, some authors refer to Buwenia and 

 Stangeria as having anastomosing veins, but the occurrence of 

 anastomosis in the segments of the former genus is denied by 

 Engler 3 and others. The proximity and number of the veins in 

 a pinna are characters of no little value in the separation of specific 

 forms, but the difficulty of eliminating the effects of fossilization 

 and the different appearances presented by the upper and lower 

 faces, render it difficult to arrive at any very trustworthy con- 

 clusion as to venation characters. In speaking of cycadean venation, 

 Borneinaun 4 suggests that the characteristic veins of Zamia have 



1 Dyer (1). 



2 (A.) Foss. Flor. vol. ii. p. 103. 



3 Engler and Prantl, p. 9. 



4 Loc. cit. p. 39. 



