36 DIOONITES. 



Brongniart points out that subsequent writers have applied his 

 generic name to plants which do not conform to the original 

 definition. He considers the essential characters to be (i.) a slight 

 union of the bases of the pinnae ; (ii.) the quadrilateral, oblong, 

 or linear form of the segments ; (iii.) truncately terminated 

 segments; and (iv.) the presence of fine parallel veins not convergent 

 at the apex. Morris * speaks of Pterophyllum as including plants 

 with pinnate fronds and sublinear pinna3, inserted by the whole 

 base, with the apices truncate or sometimes acute, etc. Miquel 2 

 keeps closely to Brongniart's original definition. Gb'ppert 3 adopts 

 a wider definition, and includes in this genus plants with obtusely 

 and acutely terminated pinna?, etc. Bornemann, 4 in 1856, defined 

 the genus as follows : " Frond pinnate or deeply pinnatisect, 

 pinnae approximate, and with the whole base attached to the 

 rachis, short, broad, quadrate, or elongate, straight at the tip 

 or obliquely truncate, horizontal or oblique to the rachis ; veins 

 parallel." 



Leckenby 5 assigns the name Pterophyllum to the species 

 P. medianum, Leek., with its Nilssonia-Vike lamina, which is 

 apparently not attached to the side of the frond axis. Schenk, 

 in his Fossile Flora der Grenzschichten 6 . . . , adopts a very com- 

 prehensive definition, and defines the pinnae of Pterofihyllum as 

 distichous, elongate, or adherent, narrow or broad, apex acute or 

 truncate ; but he says nothing as to the manner of attachment 

 to the rachis. He includes P. incrustans, Gb'pp., and P. Itraunii, 

 Gbpp., in the same genus. Heer 7 prefers the genus Zamites, used 

 in an unusually wide sense, for such fronds as his Z. borealis, 

 Heer, Z. acutipennis, Heer, etc., which resemble in general form 

 the leaves of the Wealden species originally described by Dunker 

 as Cycadites Morrisiamis. Schimper separates the fronds with 

 irregularly pinnatifid leaves from the true Pterophyllum type, and 

 institutes for their reception the genus Anomozamites. 8 In the 



1 (1),P- 118. 

 (1), P. 73. 



3 (1), P- 129. 



4 p. 58. 



5 Loc. cit. p. 77, pi. viii. fig. 2. 



6 (A. 1), Fl. foss. Grenz. Keup. Lias, p. 163. 



7 Fl. foss. Arct. vol. iii. p. 66, pi. xv. 



8 Trait, pal. veg. vol. ii. p. 140. 



