86 On the Leaf Scars of Lepidodendron. 



rhomboidal j it is usually described as rhomboidal. The 

 figures on plates V and VI give the normal shape, which 

 should be described as rhombic-trapezoidal, or what is perhaps 

 more precise, rhombic-trapeziform. The gTeatest breadth may 

 be either vertical or horizontal. In the perfect vascular scar, 

 the inferior angle is always acute. But as regards the 

 superior and lateral angles, there is so great variety-that it is 

 quite impossible to generalize. I refer the reader to the 

 figures. The superior and lateral angles are very rarely, if ever, 

 absolutely pointed, although they are frequently so figured. 

 The shape of the vascular scar seems to be somewhat affected 

 in the same manner as the general leaf scar containing it (Fig. 

 4, PI. V ; Figs. 1, 3, 4, 5, PI. VI ; Fig. 4, PI. X). 



The vascular bundles, proceeding from the vascular cylinder 

 through the thick cortical layer to the leaves, gave to the 

 vascular scars a firmer texture and more enduring character 

 than is possessed by other portions of tbe general cicatrix. 

 Consequently the vascular scars sometimes remain quite intact, 

 while the remainder of the general scar becomes somewhat 

 decorticated. L. obscurum, Lesq., described in the report of the 

 Illinois State Geol. Survey, is probably a case of this kind. 

 The same thing may very possibly occur in other species than 

 aculeatum. Prof Schimper unites L. obscurum with L. diplote- 

 gioides, Lesq. Sometimes a part of the general leaf scar 

 immediately beneath the vascular scar seems to partake of 

 the permanence of the latter, and remains as an oval or sub- 

 rotund convex elevation above the decorticated general surface 

 (Figs. 3, 5, 6, PI. VII). This is doubtless L. mammillatum, 

 Lesq., occurring with L. obscurum. 



It is not very rare to find the inferior angle of the vascular 

 scar cut away or truncate, thus giving the vascular scar a 

 conical form (Fig. 1, PI. VIII). The angle that is cut off is 

 sometimes wholly effaced ; but in some instances it remains 

 slightly separated from the main^portion of the vascular scar. 

 Prof. Lesquereux has called this distorted form L. conicum 

 (Fig. 2, PI. VIII), and remarks that, " though well marked and 

 distinct, it may be a decorticated impression." Prof. Schimper 

 says of it: " Je ne pense pas que cette espece soit distincte du 



