344 TJIE rOTOMAO OR YOUNGER MESOZOIC FLORA. 



mania ; Frenelopsis, represented by Frenela in New Holland ; Cephalotax- 

 opis by Cephelalotaxus, in China and Japan ; and Baicropsis, by Gwb/o in 

 Japan. The same is true of a number of the ferns, cycads, and protea- 

 like angiosperms. 



While Naffciopsis has not been recognized outside of the Potomac for- 

 mation, yet some of the species are much like fossils previously known 

 and described under other names. There are a number of species of 

 rodosamites that resemble some of the forms of Na(/ciopsis, which it is not 

 worth while to mention. Zaniifes Gwpperti Schenk, however, from the 

 Wernsdorf beds, is so much like Nar/ciojjsis hngifolia tliat it is difficult to 

 think that it is a different plant, while N. latlfolia seems to belong to the 

 same broad-leaved coniferous type as the rodosamites Beinii of Geyler. 



Fcildeniopsis : This is a decidedL}' recent element, being near Heer's 

 Miocene FeUdenia. 



Phjjllodadopsls .- This might be placed with Narfelopsis, etc., among the 

 types which are represented most nearly among living plants by restricted 

 genera in the Chino-Australian region, as it finds its nearest kin in PJiijUo- 

 dadus of New Zealand, Borneo, and Tasmania. V>\\t both Fcildonopsis 

 and PluiUodadopsis are too rare in tlie Potomac flora to have much impor- 

 tance. So far as they go, they indicate a more recent age for the formation. 



Baicropsis .- Tiiis is a very important genus in the Potomac, but 

 owing to the fact that it is a peculiar type, confined to the flora of that for- 

 motion, it can be of little help in determining age. Tiiis is one of the most 

 widely diffused and characteristic t3'pes found in the formation. The fan- 

 shaped and split-leaved Gingkos form a group eminently characteristic of 

 the later Jurassic and Wealden. Possibly Baieropsis is a descendant of 

 Ginhgopliyllum, and if so, its presence is quite com])atible with the Neoco- 

 mian age of the flora which contains it. 



Baiera: This is most characteristic of the Jurassic, l)nt it is too spar- 

 ingly present to have any importance. 



Frenelopsis : This genus has all the characters that would give a fossil 

 })lant weight in a flora. It is well chai-acterized, well distributed, and very 

 abundant at some localities. Frenelopsis parccramosa is very near to the 

 Neocomian F. Jlolienefjijcri, and the genus is confined to the Wealden and 



