1865.] DAWSON- COAL-rORMATIOX. 129 



(2.) Rhttidolepis (continued) Sigillaria pachyderma, Broiign. 



flexuosa, L. Sf H.'i 



elongata, Brongn. 



(3.) SiGiLLAEiA, Brongn reniformis, Brongn. 



Brownii, Dawson. 



IsDvigata, Brongn. 



planicosta, Daiuson. 



catenoides, Dcavson. 



striata, Dcavson. 



eminens, Dawson. 



(4.) Clathraeia, Brongn Menardi, Brongn. 



(5.) Leiodeema, Ooldenh Sydnensis, Dawson. 



(Asolanus, Wood). 

 (6.) SxEiNGODENDEOif, Stemh. . . organum, L. ^ H. 



Of these, seven are probably new species, and the remainder can be 

 identified with reasonable certainty with European species. The 

 differences in the markings in different parts of the same tree are, 

 however, so great, that I regard the greater part of the recognized 

 species of Sigillarice as merely provisional. Even the generic limits 

 may be overpassed when species are determined from hand speci- 

 mens. A fragment of the base of an old trunk of ^^igiUaria proper 

 would necessarily be placed in the genus Leloderma, and a young- 

 branch of Favidaria has all the characters of the genus Clathraria. 

 It is, however, absolutely necessary to make some attempt at generic 

 distinction among the diverse forms included in the genus Sigillaria ; 

 otherwise it will be impossible to reconcile the conflicting statements 

 of ajithors as to the dimensions, habit of growth, foliage, roots, and 

 fructification of these singular plants ; — such statements usually ap- 

 plying to one or more of the subordinate generic types. I shall 

 therefore notice separately, and with especial reference to their 

 function in the production of coal, the several generic or subgeneric 

 forms, beginning with that which I regard as the most important — 

 namely, Sigillaria proper, of which, in Nova Scotia, I regard the 

 species which I have named S. Broivnii (figs. 15 to 20, PI. YI.) as 

 the type. Other species are represented in figs. 21 to 28. 



In the restricted^: genus Sigillaria the ribs are strongly developed, 

 except at the base of the stem ; they are usually much broader than 

 the oval or elliptical tripunctate areoles, and are striated longitu- 

 dinally. The woody axis has both discigerous and scalariform tissues, 

 arranged in wedges, with medullary rays as in exogens * ; the 

 pith is transversely partitioned in themanner of Sternhergia ; and 

 the inner bark contains great quantities of long and apparently very 

 durable fibres, which I have, in my descriptions of the structures in 

 in the coal, named " bast tissue." The outer bark was usually thick, 

 of dense and almost indestructible cellular tissue. The trunk when 

 old lost its regular ribs and scars, owing to expansion, and became 

 furrowed like that of an old exogenous tree. The roots were Stig- 

 marice of the type of the ordinary S. ficoides. 1 have not seen the 



* Quart. Journ. Geol. Soc, paper on Structures of Coal. 



