444 <i. li. Wielandr—WiUiamsonian Tribe. 



a species of Cycas, while no cycadacean cones whatever were 

 recovered. 



But precisely because there is mixed alignment, we must not 

 go beyond the data of inference accurately enough applying to 

 eycad vegetation in bulk, and arbitrarily declare a given genus 

 with all its species to be Williamsonian. Moreover, it must be 

 equally obvious that in strong contrast to the non-determina- 

 tive or non-taxonomic results of the past fifty or more years, 

 the generic and family groupings are destined to soon undergo 

 much and even rapid change. Indeed the Greenland form 

 Cycas Steenstrupi, so long familiarly cited as a true boreal 

 Cycas, has already been found by Nathorst to represent a 

 hitherto unsuspected new genus Pseudocycas of uncertain 

 family reference ; while Zamia-like leaves have been found 

 closely associated with carpophylls (American Fossil Cycads, 

 reference 104). 



If we call to mind, however, the comparative paucity of 

 cycads of any kind in the Tertiary, and the certainty that very 

 few Williamsonias passed beyond the Cretaceous, it does seem 

 a fair inference that these latter not only made up the great 

 bulk of Mesozoic cycadophytean vegetation, but that contrary 

 to all previous views, true Cycadacese have never been mark- 

 edly more abundant in species at any time in the past than 

 they are to-day. 



Briefly told there are, omitting aberrant little-known forms 

 lilce the bipinnate Ctenis, and the older CordaitesAike forms, 

 about a dozen more or less indefinitely separable genera of 

 representative Cycadophytean leaves with either direct or 

 analogic evidence of Williamsonian affinity. Their general 

 foliar relations, culmination and extinction, may be simply set 

 forth as in the two subjoined tables : 



I. The Williamsonian Alliance. 



Pterophyllum Series : 

 (Pinnule base entire) 



Pterophyllum 

 Pioonites (?) 

 J¥ilsso)iia (?) 

 Wielandiella 



Zamites Series : 

 (Pinnule base contracted) 



Podozamites Sphenozamites 



Ptilophyllum Glossozamites 



Zamites Sewardia 



Otozamites Pictyozamites 



