246 MESOZOIC FLORAS OF UNITED STATES. 



ered it in great abundance in the basal l^eds of the lower Potomac of 

 Virginia, in that portion of the formation which Professor Ward has named 

 the "James River series." In the Virginia strata it is confined to the 

 lowest beds, and when found the cr_ystalline floor is but a few feet beneath. 

 It occurs in clay lenses in sand. It is so abundant in some places that 

 the clay is filled with the remains of the plant. These clays have in 

 many cases so well preserved the plant that the epidermal tissue is 

 intact, as also much of the rest of the plant, so that it can be peeled off 

 from the stone. It has been found also in the Glen Rose beds of the 

 Comanche series of Texas. The plant occurs in great abundance at 

 numerous localities in strata of Neocomian age in Japan. These fossils 

 were first described by Nathorst, and later by Yokoyama. Seward, in 

 his account of the Wealden flora in the British Museum, states that he 

 finds numerous fine impressions of this plant in that flora. It is quite 

 probable that the plant does occur in the British Wealden flora, but in 

 m}^ opinion the forms on which he lays much stress are not Dioonites 

 Buchianus. The reasons for this opinion will be given further on. 



The finding of this plant and similar forms of late in different 

 regions has led to a difference of opinion as to the proper naming of this 

 interesting and important genus. I have had exceptional opportunities 

 to study this plant. There is no doubt that, with the possible exception 

 of Japan, it exists in the Virginia beds in greater abundance and better 

 preserved than anj^where else. I have seen hundreds of specimens in all 

 conditions of preservation. Often the fossil, as disclosed b}^ careful 

 stripping of the rock, was much more perfect than any portion that could 

 be obtained for preservation. This is a great advantage that the collector 

 has over one who depends on specimens preserved in collections. I 

 have observed that this plant is much l^etter and ofteuer preserved in 

 the middle upper and terminal portions of the leaves than in any other 

 part. The result is that nearly all the specimens figured by myself and 

 those given by others come from such parts. The specimens shown in 

 the thin clay layers found, forming numerous interstratifications with 

 sand layers, in the banks of Dutch Gap Canal were sometimes 18 inches 

 long. They could be obtained only in smaller fragments. The leaves 

 must originally have been 2 or 3 feet long. Xot much importance is to 

 be attached to the amount of obliquity in the position of the leaflets 



