52 NTLSSONTA.. 



fertile specimens ; but in a later work l by this author we find 

 Nilssonia placed close to Pterophyllum in the Cycadacece. 



Without following in further detail the various descriptions 

 or definitions of this genus, we may thus sum up the chief 

 characters by which the species may best be recognized : 



Frond coriaceous, the lamina more or less deeply pinnatifid, 

 the lines of division generally extending almost to the rachis ; 

 segments attached to the upper surface of the axis by the 

 entire base, contiguous, usually broad and truncate, but varying 

 considerably in size and shape ; apices obtuse or truncate. Veins 

 simple and equal. 



In connection with Nilssonia, which may best be considered 

 as a genus of doubtful affinity, but probably cycadean, there are 

 three other genera of which some mention must be made, 

 Anomozamites, Pt-ilozamites, and Pterophyllum. As regards the 

 last, Nathorst has on several occasions emphasized the distinct 

 difference as regards the manner of attachment of the leaf 

 segments; in Pterophyllum they are inserted laterally on the 

 rachis ; in Nilssonia, as in Dioonites, they are attached to the 

 upper face of the leaf axis. 2 The genus Anomozamites was 

 instituted by Schimper 3 for certain species of Pterophyllum with 

 irregularly pinnatifid leaves, and this term has been generally 

 adopted ; the veins are described as simple and parallel, and the 

 segments as laterally attached. Nathorst, however, has instituted 

 a genus, Ptilozamitesf in which are included pinnate and bipinnate 

 fronds, which in habit correspond fairly closely with Anomozamites, 

 but differ in the possession of forked veins which dichotomize 

 at the base, and occasionally branch a second time before reaching 

 the margin of the leaf segment. The plant originally described 

 by Leckenby as Ctenis Leckenbyi, 5 the specific name having been 

 suggested by Bean, shows very clearly the characters of the 

 venation and the branching habit of the frond ; this must now 

 be included in Nathorst' s Ptilozamites 6 as suggested by the author 



1 (A.), Zittel, Handbuch. p. 225. 



2 Nathorst (2), p. 61, ami (A. 3), Denkschr. k. Ak. AViss. vol. Ivii. p. 45. 



3 (A.) Trait pal. veg. vol. ii. p. 140. 



4 (A. 1), Flor. Hb'ganas oeh Helsingborg, p. 21. 



5 (A.), Quart. Journ. Geol. Soc. vol. xx. p. 78, pi. x. fig. 1. 



6 Nathorst (A. 1), Flor. Hoganas, p. 21. 



