xv] 



KNORRIA 



125 



France, shown in fig. 156, affords some excuse for the institu- 

 tion of several generic names for different states of preservation 

 or decortication of one species. The cortical level exposed at e 

 is characterised by spirally disposed peg-like ridges with trun- 

 cated apices : it is this form of cast which is usually designated 

 Knorria. The ridges vary in size and shape in different types 



^s f> 



Fig. 156. A diehotomously branched Lepidodeiidioid stem (Knorria mirabilis 

 Een. and Zeill.). (After Renault and Zeiller.) (J nat. size.) The 

 original specimen is in the Natural History Museum, Paris. 



a g, surface features exposed as the result of different degrees of 



decortication. (See vol. i. p. 102, fig. 23). 



of stem ; they may be narrow as shown at e, fig. 156, or short 

 and broad with rounded distal ends. In some cases they are 

 forked at the apex, as in the partially decorticated specimen 

 of Lepidodendron Veltheimianum represented in fig. 185, A. 



The Knorria state represents the impression or cast of the 

 outer cortical region too deep below the leaf-cushion region to 



