DIOONITES. 45 



pinna is clearly shown ; and in Fig. 5 a section of a pinna 

 illustrates the strongly revolute form of the margins. Lemaire's 

 figure of this species is very poor, and gives an imperfect idea 

 of the habit of the leaf. 1 



Another species of this recent genus, E. cycadifolius, Lehm. 

 (PI. XIII. Fig. 6), also illustrates a point of contact between 

 existing and extinct fronds ; it differs from E. Ghellinckii in its 

 somewhat broader pinnae. It would, however, tend to a mis- 

 conception of the true nature of the Wealden fronds, if the 

 generic term Encephalartos were adopted on the strength of the 

 striking similarity as regards the character of the fronds ; we 

 unfortunately know nothing as to the flowers and stems of 

 Dioonites Dunkerianus. We may adopt a slightly emended form 

 of Schenk's definition for the present species : 



Frond pinnate, rachis strong, pinnoe approximate, thick, linear, 

 entire, alternate or subopposite ; 2-3 mm. broad at the widest 

 part, with a length of 11 cm. or more, gradually but slightly 

 narrowed towards the distal ends ; the two rows of pinnse 

 attached close together to the upper surface of the rachis ; the 

 lower margin of the basal end of the pinnas either slightly 

 decurrent, especially towards the tip of the frond, or somewhat 

 broadened and bluntly rounded ; towards the apex of the frond 

 the segments are obliquely inclined, and in the lower portion 

 almost at right angles, to the axis. Veins usually indistinct, 

 5-6 parallel equal veins in each pinna. 



V. 3218. PI. III. Fig. 6. 



23 cm. in length. The upper surface of the pinnaB strongly 

 convex ; pinnaB slightly and gradually tapered towards a pointed 

 apex. The arrangement of the segments and their somewhat 

 broadened bases are very similar to those in Cycadites Saporta. 

 Schenk speaks of the pinnaB as 4-4^ cm. long, but his figure 

 represents some with a length of 8 or 9 cm. In the present 

 specimen the longest pinna has a length of 1 1 cm., and this does 

 not include the actual apex. In nearly all the segments it is 

 impossible to make out the venation, but in one or two cases 

 the parallel veins are visible. Ecclesbourne. Rujford Coll. 



1 Lemaire, pi. Dlxvii. 



