266 PTERIDOPHYTA. [CH. 



attempt any specific diagnosis on such fragmentary material. 

 It is questionable, indeed, if these detached fossil leaf-sheaths 

 should be designated by specific names. Another similar form 

 of sheath, hardly distinguishable from Zeiller's species, has re- 

 cently been described by Potoni^ from the Permian (Rothlie- 

 gende) of Thuringia. 



3. Eqidsetites zeaeformis (Schloth.)' Fig. 58, E. 



The sheaths consist of linear segments fused laterally as in 

 Equisetum. In some specimens the component parts of the 

 sheath are more or less separate from one another, and in 

 this form they are apparently identical with the leaves of 

 Calamites {Calamitina) varians, Sternb. The example shown in 

 fig. 58, E is probably a young leaf-sheath ; the segments are fused, 

 and each is traversed by a single vein represented by a dark 

 line in the figure. The regular crenulated lower margin is the 

 base of the sheath, and corresponds to the upper portion of 

 fig. 58, A. This species affords, therefore, an interesting illus- 

 tration of the difficulty of separating Equisetites leaves from 

 those of true Calamites. Potoni^ has suggested that the leaf- 

 sheath of a young Calamite might well be split up into distinct 

 linear segments as the result of the increase in girth of the 

 stem. 



Other Palaeozoic species of Equisetites have been recorded, 

 but with one exception these need not be dealt with, as they do 

 not add anything to our knowledge of botanical importance. 

 The specimen described in the Flore de Commentry as Equi- 

 setites Monyi, by Renault and Zeiller^, differs from most of the 

 other Palaeozoic species of Equisetites, in the fact that we have 

 a stem with short internodes bearing a leaf-sheath at each 

 node divided into comparatively long and distinct teeth. 

 This species presents a close agreement with specimens of Cala- 

 mitina, but Renault and Zeiller consider that it is generically 

 distinct. They suggest that the English species, originally 



1 Potonie (93) p. 179, PI. xxv. figs. 2—4. 



■- Eeuault and ZeiUer (88) p. 396, PI. lvii. fig. 7. 



