XXXIX] PTEROPHYLLTJM 549 



on the upper face of well-preserved specimens, while in Ptero- 

 phyllum the continuity of the lamina is broken by a greater or 

 less breadth of rachis in the middle line of the frond ; the lamina 

 does not cover the rachis but is attached laterally, or at least the 

 two laminae of the frond, whether entire or deeply dissected, 

 do not meet in the middle of the rachis. A specimen from the 

 Cretaceous of Greenland described by Heer as Pterophyllum 

 concinnum 1 and now in the Stockholm Museum is probably a 

 piece of a Nilssonia; the rachis is not exposed on the surface 

 of the frond. In Nilssonia the veins are with few exceptions 

 simple ; in Pterophyllum they are often branched especially near 

 their origin from the rachis: in Nilssonia the segments are of 

 unequal breadth; in Pterophyllum they are usually equal. It 

 has been the practice of several authors to follow Schimper 2 

 in the employment of the generic name Anomozamites for fronds 



FIG. 610. Pterophyllum Jaegeri. From the Keuper of Lunz; part of a frond 

 23-5 cm. long and incomplete. (British Museum, V. 1044; nat. size.) 



with a more or less entire or irregularly pinnatisect lamina which 

 bear a very close resemblance to Nilssonia except that a portion 

 of the rachis is exposed on the upper face. Potonie 3 used Ptero- 

 phyllum in a wider sense including both fronds with equal pinnae 

 and those of the Anomozamites type : this more extended use of 

 Pterophyllum is adopted by Zeiller 4 who prefers to retain Anomo- 

 zamites only as a sub-genus. It is in this sense that the following 

 definition is framed. 



Fronds pinnate; pinnae linear, attached by the whole base, 

 which may be enlarged ; the apex is truncate, rounded, or occasion- 

 ally pointed; the veins are simple or dichotomously branched 

 and parallel to the edge of the lamina. In some fronds (sub-genus 

 Anomozamites) the segments are unequal (fig. 615), short, broad 



1 Heer (75) ii. PL xv. fig. 11. 2 Schimper (72) A. p. 140. 



3 Potonie (99) B. p. 281. 4 Zeiller (03) B. p. 174. 



