156 LEPIDODEXDKOX. 



Anatomy of the stem. Pith, well marked, parenchymatous, 

 or more rarely absent. Primary wood centripetal, composed of 

 scalariform tracheides, with or without conjunctive parenchyma, 

 either occupying the periphery of the pith, or, where a definite pith 

 is absent, forming the central portion of the vascular cylinder. 

 Secondary wood not always present, but, where it occurs, developed 

 centrifugally on the outer margin of the primary wood, composed of 

 scalariform tracheides. Cortex usually differentiated into two or 

 more zones, the inner composed of thin-walled tissue, and the 

 outer, consisting mainly of a periderm of thickened elements. 



Lepidodendron is one of the most characteristic genera of the 

 Carboniferous rocks of Europe and elsewhere in the Northern Hemi- 

 sphere. It appears first in the Devonian, and extends to the 

 Permian. 



In addition to casts or impressions of the true external surface, 

 others occur which are derived from more or less decorticated 

 stems. Generic names, such as Aspidiaria, were at one time 

 assigned to such fossils before their true nature had been fully 

 realized. The name Knorria is one of these, which is still sometimes 

 used to denote a particular type of Lepidodendroid cast, formed 

 internally to the bark, which has remained as a hollow cylinder 

 after the decay of the woody tissues. The features of such a cast 

 are consequently the reverse of those exhibited by the inner surface 

 of the ring of bark. 



1. Lepidodendron Pedroanum (Carruthers). 



(PL I, Fig. 2.) 



1869. Flemingites Pedroanus, Carruthers, Geol. Mag., vol. vi, p. 151, pi. v. 



1895. Lepidodendron Pedroanum, Zeiller, Corapt. Rend., vol. cxxi, p. 962. 

 L. Pedroanum, Zeiller, Bull. Soc. Geol. France, ser. in, vol. xxiii, 



p. 607, pi. viii, figs. 1-4. 



1896. L. Pedroanum, Bodenbeuder, Zeitsclir. deutsch. geol. Gesell., 



vol. xlviii, table opposite p. 772. 

 1898. L. Pedroanum, Zeiller, Conrpt. Rend., vol. cxxvii, p. 246. 



Type. V. 230. Geol. Dept. British Museum (Nat. Hist.). 



Leaf-cushions and leaf-scars rather small, somewhat varied in 

 length and breadth, in the type-specimen recalling in shape those 

 of Lepidodendron Veltheimianum, Sternb. Leaf-cushions contiguous, 

 lateral angles rounded. Leaf-scar placed at about one-third of the 



