XXXIX] PSETTDOCYCAS 559 



those of the recent genus. As thus defined, including the charac- 

 ters of the epidermal cells, the genus has no representatives; 

 but the generic name should also be apphed, as Miss Holden^ 

 has recently suggested, to fronds of the Oycas form which afford 

 no information with regard to the structure of the epidermis. 

 The resemblance of Cycadites fronds to those of Cycas, coupled 

 with the fact that impressions superficially resembhng megasporo- 

 phylls of the recent genus are recorded from Mesozoic strata, 

 was considered sufficient justification for the employment of a 

 name implying close affinity to or even generic identity with 

 Cycas. A fuller knowledge of the epidermal characters of some of 

 the fronds hitherto included in Cycadites has necessitated the 

 substitution of a new genus for Cycadites. An examination by 

 Nathorst^ of Heer's Lower Cretaceous Greenland species Cycadites 

 Steenstrufi and of other fronds showed that the epidermal cell- 

 walls are sinuous and the stomata arranged differently from those 

 of Cycas. For these and other reasons Nathorst proposed a new 

 name Pseudocycas. He also pointed out that the pinnae in the 

 fossil fronds have as a rule a double 'midrib.' Nathorst's dis- 

 covery raised the question whether other fronds described as 

 Cycadites should be transferred to Pseudocycas. Miss Holden's 

 iiivestigation of other supposed Mesozoic representatives of 

 Cycas leads to the conclusion that 'it is not impossible that all 

 Mesozoic specimens of Cycadites will turn out to be Pseudocycas.' 

 This observer shows that Cycadites Saportae Sew. and C. Roemeri 

 Schk. agree in the sinuous walls of the epidermal cells with Pseudo- 

 cycas ; and so far no species of Cycadites, in which it was possible 

 to examine the cuticular membrane, has been found that does 

 not conform to Nathorst's definition of Pseudocycas at least as 

 regards the structure of the epidermal cells. Nathorst defined 

 Pseudocycas in the following sense: Fronds similar to those of 

 Cycadites and Cycas but with pinnae characterised by a double 

 'midrib,' the stomata being confined or almost confined to the 

 groove between the two 'midribs.' Nathorst also notes that in 

 Pseudocycas the bases of the pinnae are not contracted as is often 

 the case in Cycadites and Cycas, but this is a feature of secondary 

 importance. Miss Holden has, however, expressed the opinion 

 1 Holden, R. (U^). " Nathorst (078). 



