282 TflE POTOMAC OR YOUNGEE MESOZOIC FLORA. 



exists ; petioles proportionally very thick and apparently succulent ; ner- 

 vation of the primary order very slender, and with little or no difference in 

 the strength of the primary nerves ; reticulation of all orders lax, irreg- 

 ular in shape, and varying in the size of the meshes; ultimate nerves strong, 

 all of equal strength and fern-like. These leaves form an important por- 

 tion of the angiosperms that occur with a predonu'nant floi'a of Jurassic 

 type, as at Fredericksburg, and they give a very ancient look to the angio- 

 spermous element of the flora. 



Prote^phyllum reniforme, sp. nov. 



Plate CXXXIX, Fig. 3 ; Plate CLVI, Fig. 4 ; Plate CLX, Figs. 1, 2. 



Leaves small, reniform, inequilateral ; leaf-substance quite thick ; pet- 

 iole proportionally very thick and apparently succulent, splitting up on 

 entering the leaf into a number of nearly equal primary nerves, which, 

 repeatedly subdividing in a palmate manner and anastomosing, fill the 

 leaf with a very irregular lax reticulation, the branches being nearly of 

 equal strength with the primary nerves ; ultimate reticulation not seen. 

 The smallest reticulation seen is formed by comparatively strong branches, 

 that generally make large, nearly right angles with their parent nerves. 

 The branches of the primary nerves go off very obliquely. 



Localities: Fredericksburg; 72d mile-post ; fishing hut above Dutch 

 Gap Canal ; rare. 



The imprint given in PI. CXXXIX, Fig. 3, represents the entire leaf. 

 On the right-liand lower side it has been pressed upwards from below so as 

 to roll over the lower margin of the leaf upon the nerves, making the out- 

 ermost of them appear to issue from a marginal nerve. This pressure has 

 probably produced also a distortion of the primary nerves in the left-hand 

 half of the leaf, crowding them together abnormally. The thick substance 

 makes it difficult to follow the iiltimate nervation. Plate CLX, Fig. 1, 

 gives a large fragment of a leaf much mutilated and wrinkled transversely. 

 This specimen, presenting its lower surface uppermost shows tlie nerves 

 much more distinctly. It shows that the penultimate meshes seen are sub- 

 rhombic in shape, being made by nerves meeting mostly under acute 

 angles, but the ultimate or smallest meshes are irregular, subrotund, or 



