58 EQTJISETITES. 



diaphragms of Calamites developed a layer of cork -tissue, and 

 Jeffrey 1 has more recently described the partial sclerification of 

 periderm cells in the diaphragms of recent Horsetails. 



The specimen (No. 10,379) represented in PL XIX. Fig. 4 

 affords a good example of an isolated nodal diaphragm, and in 

 Pig. 5 of the same Plate a portion of a similar diaphragm is 

 surrounded by an imperfectly preserved leaf-sheath ; the latter 

 specimen, from the Leckenby Collection, 2 demonstrates the nature 

 of the discs, and shows that their usual manner of occurrence 

 a little distance above the node is merely the result of displace- 

 ment. As the hollow branches were crushed by the weight of 

 overlying sediment the diaphragms, being comparatively resistant, 

 were squeezed from their original position and flattened out on 

 the intemode. 3 



It has been the custom to regard the form named by Phillips 

 Equisetum later ale as specifically distinct from Brongniart's species ; 

 but a comparison of numerous specimens of Equisetites columnaris 

 and E. later alis has led me to unite both under Brongniart's 

 designation. Nathorst inclined to this view, as shown by a note 

 written on a specimen of E. lateralis in the Leckenby Collection 

 " Eq. columnaris includes Eq. lateralis" The difference in diameter 

 between the smaller examples of E. lateralis and the ordinary casts 

 of E. columnaris is considerable, but in a large collection it is easy 

 to find intermediate forms ; the leaf-sheaths also exhibit no dis- 

 tinguishing features, but agree in the form of the segments and 

 in their minute surface features. 



The Italian specimens figured by Zigno 4 as Equisetites Veronensis 

 appear to be identical with the common British species, and his 

 species has therefore been included in the above synonymy. The 

 fragments of stems described by Saporta 5 from rocks referred 

 to a Bathonian horizon bears a close resemblance to Equisetites 

 columnaris, and may well be specifically identical ; but in the 

 absence of more satisfactory evidence than is afforded by Saporta's 



1 Jeffrey (99), p. 176. 



2 Leckenby Collection, Cambridge, No. 17. 



8 Specimens of nodal diaphragms may be seen in several collections of Jurassic 

 plants; e.g., Oxford, Cambridge, York, Manchester, Scarborough, etc. 

 4 Zigno (56), pi. vi. 

 * Saporta (73), p. 248. 



