OLDER POTOMAC OF VIRGINIA AND MARYLAND. 579 



latter identified three species. Two of them, Sequoia ambigua Heer and 

 S. Reichenbachi (Gein.) Heer, are important fossils in the Lower Potomac 

 of Virginia. The third is identical with a fossil described by me from 

 the Glen Rose beds of the Trinity of Texas, with the name Pagiophyllum 

 aubium." This latter plant Doctor Nathorst named Pseudofremelopsis 

 Felixi, and in describing it he made some errors which, as they may lead 

 to further errors and confusion, are noticed below. 



These facts seem to indicate that a Neocomian or Lower Cretaceous 

 age may be claimed with a good deal of confidence for the Lower Potomac 

 flora. 



So far as I am informed, the only evidence claimed to oppose the 

 conclusion that these beds are Lower Cretaceous is that presented by 

 Professor Marsh, which was derived from an examination of the verte- 

 brate fauna of the Arundel group and the Como beds. This, however, 

 simply goes to indicate the Wealden age of the strata. 



When Doctor Nathorst made his determination of the Mexican 

 plants for Doctor Felix he had not seen the paper on the Texas Glen 

 Rose fossils prepared by me, and when his paper was prepared Doctor 

 Nathorst's article had not been read by him. The result was that the 

 same species was described under two different names. However, Doctor 

 Nathorst had before him my description of FreneloiJsis parcera7nosa given 

 in Monograph XV. From certain similarities in the Virginia and Mexican 

 fossil Doctor Nathorst concluded that they are the same. From the 

 study of the Mexican plant he decided that the Virginia fossil had been 

 incorrectly diagnosed. Hence he formed a new genus, which he calls 

 Pseudofrenelopsis. Had Doctor Nathorst possessed specimens of Frene- 

 lopsis parceramosa he would never have fallen into this error. The 

 plants are quite different and probably are not nearly allied. The Texas 

 plant, which is that described by Doctor Nathorst, does not have jointed 

 branches. Doctor Nathorst assumes that I incorrectly diagnosed 

 Frenelopsis parceramosa as having jointed twigs. There is not the 

 shadow of a doubt that it has. F. parceramosa has its branches con- 

 spicuously constricted at the joints, and the latter are so marked that the 

 branches break up into small fragments by a separation at the joints. 

 Hence it is difficult to get a twig of any considerable length. 



"Fontaine, Notes on some fossil plants from the Trinity division of the Comanche series of Texas: Proc. 

 U. S. Nat. Mus., Vol. XVI, 1893, pp. 271-273, pi. xxxix, figs. 2-11. 



