334 Systematic Paleontology 



diameters) the outlines are still substantially rectangular, but the walls 

 are seen to be not straight but irregularly waved or undulatory, as shown 

 in the figure. This waving is less regular and less emphasized than in 

 similar figures given by Schenk for the genus Pterophyllum, and seems 

 to be more pronounced in the lateral and less marked in the transverse 

 walls. The cells are small, about 7 microns (2/3 obj.) in diameter, and 

 the walls are thin. The stomata are numerous and without regular 

 arrangement, but the guard cells are all oriented alike and parallel, 

 presumably to the long axis of the pinnule. This feature also differs 

 from their arrangement in Pteropliyllum, as shown by Schenk, where 



Fig. 10. — Cuticle of Dioonites Buchlanus viewed from within, X 385. 



they are less numerous and without parallel orientation. The guard 

 cells are two in number and stout in form. Their upper surface is just 

 at or slightly below the surface of the cuticle, and they are quite deep, 

 becoming nan-ower inward. These features will enable observers to 

 distinguish Dioonites from fragments of similar appearance like those of 

 Nageiopsis in cases where the cuticle is preserved. 



This fine plant is very abundant in the lower Potomac, along the 

 James Eiver in Virginia, the splendid specimens figured on pis. li and 

 lii coming from Sailors' Tavern. The remains from Maryland, which 

 have been identified as this species, are extremely poor and questionable, 

 those so identified with a query by Fontaine from the locality on the 

 Bewley estate being here omitted as undeterminable. 



