Relation Between Cycadites and Pseudocycas. 339 
When it is a question of impressions, the upper surface shows two 
ridges with a furrow between, and the lower a single furrow or two 
furrows with a ridge between. It should be noted, however, that 
in some species of Cycas, the collapse of the midrib is much delayed, 
and possibly never occurs— e.g., some herbarium specimens of 
C. revolutu in the Botany School, dated 1852, showed always a 
single ridge on the lower surface. This is illustrated in Pkwte III, 
Figs. 4 and 5—impressions of the upper and lower surfaces 
respectively of C. revoluta; slight indications of a double line maybe 
seen in Fig. 4, but none whatsoever in Fig. 5. Further, in one 
species, C. Rumphii, where the midrib normally projects from the 
upper surface instead of from the lower as in other species, the 
collapse is necessarily on the upper surface, so that herbarium 
specimens show two ridges with a groove between. Enough has 
been said to show, that granting a close analogy to exist between 
Cycadites and Pseudocycas on the one hand, and Cycas on the other, 
it is impossible to consider the presence of a single or double midrib 
as a character of any diagnostic significance. 
This brings us to the question of the difference between 
Cycadites and Pseudocycas , and unless the cuticles are available, it 
is difficult to find one. We have shown that the midrib is not 
reliable, and it seems decidedly doubtful how far the character of 
the basal attachment as described by Nathorst will hold. It is not 
impossible that all the Mesozoic specimens of Cycadites will turn 
out to be Pseudocycas. Such has been found to be the case in all 
the material investigated by Nathorst, and in all the English material 
in the Sedgwick and British Museums; further in a recent letter to 
Professor Seward, Professor Zeiller states that the French specimens 
of Cycadites which he has examined, belong probably to Pseudocycas 
At the same time, the difference between that genus and Cycas is 
considerable, and probably Tertiary fronds will be unearthed whose 
cuticular structure will show them to be directly ancestral to Cycas. 
As a possible way out of the difficulty we may suggest that in the 
future the genus Pseudocycas should include those forms whose 
cuticles have the structure described by Nathorst, and that Cycadites 
should be retained for fronds resembling the living Cycas in external 
appearance, but whose cuticles are as yet unknown. 
Summary. 
1. Cycadites Sapoyhe and C. Roemeri should be transferred to 
the genus Pseudocycas, since they differ from the members of that 
genus described by Nathorst only in the distribution of the stomata. 
