496 MESOZOIC FLORAS OF UNITED STATES. 



Menispermites tenuinervis Fontaine. 

 PI. CIX, Figs. 2, 3. 



1889. Menispermites tenuinervis Font.: Potomac Flora (Monogr. U. S. Geol. Surv., 



Vol. XV), p. 322, pi. clxxii, fig. S. 

 1895. Menispermites virginiensis Font. Ward: Fifteenth Ann. Rep. U. S. Geol. 



Surv., 189.3-94, p. 360,'^' pi. iv, fig. 7. 



No fewer than 31 specimens referable to this species occur in the 

 collections from the Mount Vernon beds. All but three are from the 

 Mount Vernon localit_y, but these three were found at White House Bluff. 

 These specimens represent a plant which appears to be specifieally dif- 

 ferent from M. virginiensis. This latter is not rare in the collections, 

 and differs in several important points from the plant now in question. 

 As given in Monograph XV, a small Menispermites, described as M. 

 teiiuinervis,^ was found very rarely on Jackson, formerly Belt street, 

 Baltimore, Md. The specimens found in Baltimore were very rare, and 

 mostly small fragments. The most complete leaf, given in fig. 8, showed 

 fully a portion of the three primary nerves. The size of the leaves and 

 the delicate nervation of the Mount Vernon specimens are points that 

 agree with the Baltimore plant, and make it probable that the specimens 

 belong to M. tenuinervis. These leaves differ markedly from those of 

 M. virginiensis, since they are generally much smaller. The nervation 

 is also much more delicate. This was probably the case with the Bal- 

 timore plant, and hence the difficulty of seeing its nervation. . The fine 

 clay of the Mount Vernon localities is exceptionall}^ well fitted to show 

 delicate details, otherwise the minor nervation would probably be 

 inconspicuous in these specimens also. The small leaf given as M. vir- 

 giniensis in pi. iv., fig. 7," of Professor Ward's Mount Vernon flora'' is 

 probably this species. The contrast between this leaf and the one rep- 

 resented in fig. 8 of the same plate illustrates well the difference between 



oFrom the statement here made it seems that Professor Fontaine, to whom some of the Mount Vernon 

 material was submitted at that time, himself referred both these leaves to his M. virginiensis. The difference 

 may not be specific. — L. F. W. 



6 Monograph XV, p. 322, pi. clxxii, fig. S. 



«The Potomac formation: Fifteenth Ann. Rep. U. S. Geol. Surv., 1895, pi. iv, fig. 7. 



f' Through inadvertence the counterpart of this specimen was drawn for this paper, and is represented 

 on PL CIX, Fig. 2. In view of the fact that Professor Fontaine refers this specimen to M. tenuinervis it may 

 be well to retain the figure. It shows the lower side of the leaf, whefe the raised nerves are more distinct than 

 they are on the upper side. — L. F. W. 



