DIOONITES. 35 



clearly preserved. The midrib and pointed apex well seen in 

 several of the pinnse. Ecclesbourne. Rufford Coll. 



V. 2924. 25 cm. long. A single row of pinna? attached to 

 one margin of the broad flat rachis; midrib distinct. Eccles- 

 bourne. Riiffurd Coll. 



Genus DIOONITES, Miquel. 

 [Tijdsch "Wis. Nat. "Wet. vol. iv. 1851, p. 205.] 



In dealing with such fronds as those figured by Bunker as 

 Cycadites Morrisianus, Dunk., and C. Brongniarti, Ro'ru., and 

 afterwards described by Schenk as species of Pterophyllum or 

 Dioonites, we have to face the difficulty of deciding upon the most 

 suitable generic term. The fronds in the Rufford Collection show 

 well-marked characters, and leave no doubt as to the form and 

 manner of attachment of the pinnae ; we have long, narrow, linear 

 and parallel-veined segments, with acutely pointed tips attached 

 by broad and non-auriculate bases to the upper surface of the 

 rachis. Must these be included in Pterophyllum or Dioonites, or 

 do the generally received definitions of these genera not admit 

 of the application of either name to the Wealden fronds ? Let 

 us briefly summarize some of the various definitions of these 

 genera, and note how far they coincide with the characteristic 

 features of the present series of specimens. Pterophyllum was 

 defined by Brongniart in 1828 ' as a genus characterized by 

 " Feuilles pinnees, a pinnules d'une largeur a peu pres egale, 

 s'inserant sur le petiole par toute la largeur de leur base, tronquees 

 au sommet ; nervures fines, egales, simple, peu marquees, toutes 

 paralleles." He speaks of the truncate apices of the pinnse as 

 an essential character, but does not insist on a lateral or surface 

 insertion on the frond axis. Pterophyllum Jaegeri, Brong., is spoken 

 of as one of the species of this genus, and in this instance the 

 attachment of the segments is apparently lateral. In the Tableau 2 



1 (A. 2), Prodrome, p. 95. 



2 (A. 4), p. 03. 



