EASTERN BORDERS. 303 



apart ; the areolae also vary in form ; when well preserved, they are 

 rhomboidal, contiguous, and spirally arranged. Buckland's U. Allani 

 and Brongniart's L. omatissimus are representations of different 

 portions of the same species. 



Genus Knorria (Stemb.). 



The fragments found of these plants are tree-like stems, covered 

 with prominences, which are the remains of thick, short, sessile 

 leaves, spirally disposed. Their mode of branching is dichotomose, 

 like that of Lepidodendron, to which they appear nearly related. 

 Sternberg considers the leaves to have been cylindrical, and similar 

 to those of succulent plants. 



Knorria imbricata (Stemb.). Ref. Stemb. t. 27. 



The leaf remains of this rare fossil are oblong, cylindrical, either 

 truncate or subacute, imbricated and adpressed. 



Localities. Alnwick Moor and Shilbottle, in sandstone. 



Knorria taxina (Lindl.). Ref. Foss. Fl. t. 95. 

 Locality. Budle, in shale. 



Plants allied to Exogens, Endogens, and Acrogens. 



Genus Calamites (Schlotheim). 



In most coal-fields, reed-like plants, hence called Calamites, are 

 abundant, and they are not unfrequent in our district. They are 

 usually found in short fragments which are jointed and furrowed. 

 Branches, also jointed and furrowed, proceeded from the nodes, gra- 

 dually thickening as they lengthened, and afterwards tapering off. 

 They seem to have possessed needle-shaped leaves, arranged in whorls 

 around the stem at the joints. The Equisetum or common Horse- 

 tail presents a similar appearance to these singular plants. The 

 Calamites, however, were of much greater magnitude ; we have seen 

 specimens from Russia above one foot in diameter. 



Mr. Dawes has recently thrown some light on the structure of the 

 Calamite, which appears to consist of a large central column of tissue 

 surrounded by a cylinder of woody structure*. The fossil as ordi- 

 narily found is, according to Mr. Dawes, a mineral cast of the inside 

 of this cylinder, which is composed of two distinct tissues, one cel- 

 lular and the other pseudo-vascular. These are arranged in alter- 

 nating vertical plates, and interrupted at intervals, corresponding to 

 the joints, by horizontal plates of tissue or Phragmata ; concentric 

 rings were observed, indicating exogenous growth ; and network of 

 quadrangular tissue similar to that of Coniferae was seen, along with 

 other rectangular cells, arranged in perpendicular series, such as are 

 more commonly met with in Endogens. The Calamite, therefore, 



* Proceedings of the Geological Society, vol. vii. p. 196, 



