508 Systematic Paleontology 



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 to 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 depressions, according to the relation of the fossil to the 

 original leaf. Depressions seem to have existed originally in the leaf 

 and these leave elevations in the clay embedding the leaf. The number 

 of these radiating inequalities 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 continuous 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 

 by the leaf. The true position of this peculiar leaf is very problematical. 

 It is placed with doubt in the genus Aristolochisephyllum.'^ — Fontaine, 

 1906. ' .. 



As suggested by Ward there is a superficial resemblance to Kaida- 

 carpum cretaceum Heer. The nature of the present form is conjectural, 

 and it may not represent a leaf at all. 



It is extremely doubtful if it bears any relation to Aristolochicephyllum 

 crassinerve. It may represent the underside of a thick floating leaf of 

 unknown aflinity. 



Occurrence. — ^Patapsco Formation. Mt. Yernon, Virginia. 



Collection. — U. S. National Museum. 



