248 MESOZOIC FLORAS OF UNITED STATES. 



Buchianus and equally plain that they are the same with the Potomac 

 fossil which I described as D. Buchianus obtusifolius." In my examination 

 of the numerous fossil specimens of D. Buchianus found in the Lower 

 Potomac beds they were found to exhibit great constancy in the mode 

 of insertion of the leaflets, when this could be made out. The only 

 rather common variation that occurred with sufficient definiteness to 

 give a basis for varietal distinction was in the narrowness of the leaflets 

 of certain forms, which did not arise from the leaflets belonging to the 

 summit of the leaves, and which did not graduate by intermediate forms 

 into the normal Buchianus type. This led me to regard these as a 

 variety (angustifolius) of the species. The separation was not based 

 upon any particular mode of narrowing of the parts of the leaflets, but 

 upon the constant recurrence of unusually narrow leaflets in the whole 

 leaf. It is quite possible that they may be young leaves of the normal 

 species. I did, however, find a single fine specimen of a plant resembling 

 D. Buchianus which presented obvious and important differences from 

 the normal forms. This is the specimen that I named D. Buchianus 

 obtusifolius. It has the leaflets inserted 07i the upper face of the midrib 

 by an articulation, and when the leaflets are separated from the midrib 

 they leave an elliptical scar. The points of difference from the normal 

 Buchianus type were so important that I hesitated long to put it in the 

 same species with this latter. As, however, I had found but a single 

 specimen with these characters, and as that occurred associated with 

 numerous normal forms, I did not feel justified in regarding it as more 

 than a variety of the species now in question. Had I found the numerous 

 specimens showing these features that Seward has seen I should have felt 

 compelled to separate it from D. Buchianus not only specifically but 

 generic ally. 



The objection to giving D. Buchianus a generic name implying 

 affinity with the living genus Zamia — such names as Zamiophyllum of 

 Nathorst, and Zamites, as proposed by Seward — do not apply in the 

 case of my D. Buchianus obtusifolius and of Seward's plants. The name 

 Zamites, however, has already been applied to too many different types 

 of fossil cycads. Such different forms as Z. Feneonis (Brongn.) Ung. 

 and Z. arcticus Gopp., it would seem, ought to be separated as at least 



a Monogr. U. S. Geol. Surv., Vol. XV, pp. 184-185, pi. clxviii, fig. 3. 



