DAWSON — BIGILLAPvIA, CALAMITES, AND CALAMODENDEON. 159 



Lepklodendra -with the Sigillarm of the Favularia-tj-pe. On the 

 other hand, as already stated under Sigillaria, the ribbed Sigillarim 

 may be related through Ormoxylon and Dadoxylon to the modern 

 Conifers, and the Favularim may be related to the Cycads. This re- 

 lationship may be expressed as follows : — 



Cycadacem. _ Coniferce. 



Dadoxylon. 

 Favularia ? Palseoxylon. 



Ormoxylon t- 

 Dictyoxylon. 



SlGILLAEIA. 



Ehytidolepis. Calamodendron. 



Favularia ? Calamopitus. 



Clathraria. . Bornia. 



Syringodendron. Calamites. 



Lepidophloios. Equisetacece. 

 Lepidodendron *. 

 Lycopodiacece. 



I do not give this Table with any view to theories of derivation, 

 but merely as an expression of probable affinities among these very 

 curious and ancient types of vegetation. 



I may add here a few words with reference to SplienopIiyUum., a 

 genus which some authors unite with Calamites. The verticillate, 

 cuneate, veiny leaves of this plant, and its spikes of fructification 

 have long been known ; and in 1865 I was enabled by a specimen 

 in the collection of Sir "W. E. Logan to determine the structure of 

 its stem, which contains a slender axis of reticulato-scalariform 

 vessels of the type of those in Tmesipteris'X . These plants obviously 

 had no connexion with Calamites or Calamodendron, but constitute 

 a peculiar synthetic type, presenting points of resemblance to Ferns 

 and Marsiliacese. 



In conclusion, and with reference to my former papers on the 

 " Structures in Coal," I would repeat the statement made in those 

 papers, that the tissues of Sigillaria, as defined in this paper, and of 

 Calamodendron enter more largely than any others into the compo- 

 sition of the mineral charcoal, and other parts retaining structure, 

 of the coal of Nova Scotia ; and I have reason to believe that similar 

 tissues are at least very abundant in the coal of this country. 



Supplementary Note. — Owing to the delay in the publication of the 

 above paper, it is necessary to add the following statements : — 



(1) Prof. Williamson has described another type of Calamitean 

 stem, which he regards as intermediate between his Calamopitus and 

 Calamodendron §, but which has the reticulated or midtiporous vessels 

 of the former. To Prof. Williamson is due the credit of recognizing 

 this structure for the first time in English specimens, though, as above 



* Including Sageomria. t Dawson, MS. 



X Quart. Journ. Geol. Society, May 1866. 



§ Manchester Lit. and Phil. Soc, Proceedings, 1870. 



