OLDER POTOMAC OF VIRGINIA AND MARYLAND. 493 



a series of cell-like meshes, separated by narrow, raised, flat borders, 

 which appear to be the nerves of the leaf. The specific name of the plant 

 is founded on the cell-like character of the spaces between these nerves. 

 The meshes cover the entire surface of the leaves. They are polygons 

 made by the meeting, under large angles, of several sides. The number 

 of the sides varies. They are mostly 5-8, but may occasionally be fewer. 

 Their size also varies, some being twice as large as others. Within the 

 meshes and grouped, radiating from a central point, are ridges or depres- 

 sions, according to the relation of the fossil to the original leaf. Depres- 

 sions seem to have existed originally in the leaf and these leave elevations 

 in the clay embedding the leaf. The number of these radiating inequal- 

 ities varies. They are mostly 5 or under. The concavities existing on 

 the leaf seem to be puckers in its thick texture. There is apparently 

 nothing like a differentiation of the nerves into grades, such as primary, 

 secondary, etc. The flat, strong, cord-like margins or sides of the cells 

 form the whole of the nervation. But some of the margins of the cells, 

 corresponding in position and placed in the central line of the leaf, are 

 so located as to seem to be continuations of one another and to form an 

 irregular flexuous midrib. This, however, is accidental, and the margins 

 of the meshes are the only nerves possessed bj^ the leaf. The true posi- 

 tion of this peculiar leaf is very problematical. It is placed with doubt 

 in the genus Aristolochisephyllum. 



As indicated by Professor Ward, on the labels accompanying this 

 plant, it has some resemblance to Heer's Kaidacarpum cretaceum, " but it 

 is clearly not a fruit, as Heer considers that plant to be. 



Celastrophyllum Brittonianum Hollick.* 

 PI. CVII, Fig. 7. 



1895. CelastropJiyllum Brittonianum HoUick in 'Newherr J : Flora of the Amboy Clays 

 (Monogr. U. S. Geol. Surv., Vol. XXVI), p. 105, pi. xlii, figs. 37, 38, 46, 47. 



1895. CelastropliyUum Brittonianum Hollick. Ward: The Potomac Formation 

 (Fifteenth Ann. Rep. U. S. Geol. Surv., 1893-94), pp. 349, 358, 377, 378, 379. 



« Fl. Foss. Arct., Vol. VII (Flora der Patootschichten), p. 19, pi. Ixiv, fig. 9b. 



^ One of the specimens collected by me on my first visit to the Mount Vernon plant bed, October 16, 1892, 

 seems certainly to be Celastrophyllum Brittonianum of Hollick, and agrees ver}' closely with his figs. 38 and 

 47. The dentation extends somewhat farther down than that of any of the leaves figured by him, but this 

 is scarcely a specific distinction. The exact shape of the base is not known, as it is unfortunately wanting, 

 but the contraction begins at the same point and probably proceeded in the same way. From the very close 

 resemblance I do not feel justified in separating it from that species, notwithstanding the difference in age, 

 and this form ma}- therefore be regarded as constituting one more of the few cases in which Older Potomac 

 species persist into the Newer Potomac or Raritan formation. — L. F. W. 



