58 EQTJISETITES. 



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

 Jeffrey' lias more recently described the partial sclerification of 

 periderm cells in the diaphragms of recent Horsetails. 



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

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

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

 surrounded by an imperfectly preserved leaf-sheath ; the latter 

 specimen, from the Lectenhy Collection,' 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.' 



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

 ^qmsetum laterdle as specifically distinct from Brongniart's species ; 

 but a comparison of numerous specimens of Squisetites columnaris 

 and a. lateralis 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 Leokenby Collection — 

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

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

 of M 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 * as jEqiisetites 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^ 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 afiorded by Saporta's 



1 Jeffrey (99), p. 176. 



* Leokenby Collection, Cambridge, No. 17. 



' Specimens of nodal diapbragme may be seen in several collections of Jurassic 

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



* Zigno (56), pi. vi. 



' Saporta (73), p. 248. 



