566 CYCADOPHYTAN FRONDS [CH. 



and Jurassic strata and specimens are recorded from the Lias 

 of Lyme Regis on the south coast of England. 



Cycadites Renaulti Lignier. 



This species, from the Middle Lias of Normandy i, is founded on 

 fronds 2-2 — 2-6 cm. broad with a rachis 3 mm. in breadth bearing 

 laterally-inserted pinnae almost at right-angles 11 — 12 mm. long 

 and 1-25 — 1-50 mm. broad; it is very similar to C. rectangularis 

 which occurs in the same beds. 



II. NiLSSONIALES. 



NILSSONIA. Brongniart. 



This genus^ was named after the Swedish naturahst Nilsson 

 who had figured certain plants from the Lias of Hor referred by 

 Fries to the Ferns: these were named by Brongniart Nilssonia 

 brevis and N. elongata and classed with the Cycads. The type- 

 specimens of the latter species are regarded by Nathorst as a 

 form of N. brevis. The history of the genus is fully discussed 

 in Nathorst's able monograph^. Nilssonia, founded on fronds 

 which with one exception are known only as casts or impressions, 

 may be thxis defined: Fronds with circinate vernation, at least 

 in the type-species Nilssonia brevis (fig. 619, C, D), similar in 

 shape to the leaves of Scolopendrium vulgare and Polypodium 

 irioides and to such unusual forms of Cycas fronds as those 

 reproduced in figs. 384, 387, I*, in which the laminae of the pinnae 

 are concrescent and form a continuous or deeply cut lamina. 

 They may reach a length of 60 cm. and a breadth of 10 cm. and 

 some specimens are known in which the leaf is less than 1 cm. in 

 width. The lamina is occasionally entire, but in the great majority 

 of cases it is more or less deeply cut into segments of imequal 

 breadth varying considerably in size and shape even in the same 

 species, usually deep and truncate and sometimes long and narrow 

 {e.g. N. pterophylloides, fig. 619, B). An important distinguishing 

 feature is the attachment of the lamina to the upper face of the 

 rachis which it covers: the extension of the lamina over the 

 surface of the frond axis and the rare occurrence of branching 



1 Lignier (13) p. 90, PI. ix. figs. 18, 19. = Brongniart (25). 



' Nathorst (09^). « Pages 13, 16. 



