2?8 Contributions towards Establishing the General Character 



the ribs of the specimen of Sifjillaria Icevipata, figured in Plate 143 of the 

 " Vegetaux Fossiles," may be considered to have been at one time no 

 wider than the leaf-scars or bases, which form so prominent a feature in 

 the figure, and at the same time display so obviously all that is required 

 to confirm the above supposition. The same may be said of S. reni/or- 

 nns (Plate 142), ^^ PoUerlana (PI. 165 ?), and a number of other wide- 

 ribbed examples which Brongniart has figured. Artis' Euphorbites vul~ 

 ffaris, shews not only the lateral parts of the ribs and the furrows to 

 have increased considerably in the horizontal direction, but also the 

 median line of the ribs, as is manifest by the vascular scars being very 

 wide apart at the base of the stem. This increase of the median line of 

 the ribs, it may be supposed, has taken place subsequently to the falling 

 off of the leaves. 



This appears a fitting moment to revert to the previously mentioned 

 remarkable character, which is displayed on one of the North Biddick 

 specimens. When describing this fossil, it will be recollected that men- 

 tion was made of the median part of the ribs on a certain place, being 

 below the level of the furrows. From what has just been urged in ex- 

 planation of the widening of the ribs, the cause of this peculiarity, I 

 think, will readily suggest itself ; for, if the lateral parts of a rib offered 

 little or no resistance to the horizontal development of the stem, com- 

 pared with what would be offered by the median part, — owing to the 

 attachment of the leaves, it seems a necessarj^ consequence that the 

 former, as well as the furrows, would occasionally grow out beyond the 

 plane of the latter. The more general fact of the furrows becoming ob- 

 solete on the base of the stems of Sigillariay is evidently attributable to 

 the same cause. 



The extreme probability of the fossils named Favularia, — at least some 

 of them, constituting neither a genus, a section of a genus, nor even a 

 distinct species, but simply the terminal portion of an individual Sigil- 

 laria, induces me to examine that section which Brongniart has termed 

 Clathraria, and known by being reticulated as the Lepidodendrons. Of 

 this section I have merely to suggest, that some of the species which it 

 includes, are probably nothing more than portions of the stems of SigiU 

 laria, belonging to those parts which have been subject to some irregu- 

 larity of growth, arising from the setting on of the branches or otherwise. 

 No one who has paid any attention to those species of Conifera, whose 

 stems are fluted as it were, can have failed in observing, that wherever 

 an irregularity of growth of the kind just alluded to has taken place, 

 their surface becomes more or less reticulated. It is probable, however, 

 that some of the specimens which are figured in the " Vegetaux Fossiles," 

 taay belong to plants completely so characterized ; in this case, they 

 would appear to constitute a more cycadoidal group than the true Sigil- 

 larice. 



