572 CYCADOPHYTAN FRONDS [CH. 



sessile. Between the regular grooves on the upper surface the 

 lamina is more or less convex; seen from below the grooves are 

 represented by ridges and between each pair of ridges there are 

 parallel folds, sometimes three (fig. 620, B) or as many as six; 

 and where the segments are narrow, that is the strips of lamina 

 between two grooves (or ridges), there may be only a single fold 

 which gives the appearance of linear segments with a single 

 midrib as in Cycadites, a misleading resemblance of special interest 

 in reference to the Nilssonia fronds described by Oldham and 

 Morris 1 and by Feistmantel 2 as Cycadites rajmahalensis. Owing 

 to the fleshy nature of the leaf the difference between the upper 

 and lower side is particularly well marked in this species. The 

 lamina may be more or less entire, but is usually divided by deep 

 sinuses extending to the rachis into truncate or distally tapered 

 segments varying in breadth (fig. 619, C, D), the narrow segments 

 being characterised by a more pointed apex than in N. polymorpha. 

 The structure of the stomata and epidermal cells is of the type 

 described in the definition of the genus. Strongly cuticularised 

 papillae, incorrectly described by Schenk 3 in N. polymorpha as 

 stomata, occur on some of the epidermal cells : these may be the 

 bases of hairs. In some preparations Nathorst found patches 

 of a resinous substance, an interesting discovery in view of the 

 occurrence of secretory canals in the petrified leaf of Nilssonia 

 orientalis described by Dr Stopes 4 . 



Nilssonia brevis occurs in Upper Ehaetic and Lower Liassic 

 strata. 



Nilssonia pterophylloides Nathorst. 



A Rhaetic Scanian species originally referred by Nathorst 5 

 to Nilssonia but later removed by him to Dioonites Q and in 1909 

 reinstated in Nilssonia 7 on the ground that the lamina covers 

 the upper face of the rachis. The segments are fairly uniform 

 in breadth and linear; they reach 10 cm. in length and are usually 

 5 7 mm. broad ; the lamina is slightly tapered towards the 

 apex (fig. 619, B). There are 3 10 parallel grooves on the upper 



1 Oldham and Morris (63) Pis. vn., vin. 2 Feistmantel (77 3 ) p. 124. 



3 Schenk (67) A. PI. xxix. fig. 10. 4 Stopes (10 2 ). 



5 Nathorst (86) p. 72. 6 Ibid. (02) p. 18, PL i. 



7 Ibid. (09 2 ) p. 21, Pis. vi., vii. 



