of the Fossil Plants of the genus Sigillaria. 15 



middle scar of each series is very small, compared with those lateral to 

 it ; and hence they have rather the appearance of being in pairs. Brong- 

 niart's figure of Sigillaria laevigata, shews the triple nature of the series 

 where the specimen is decorticated. Now, as each series of scars un- 

 doubtedly resulted from one bundle of vessels passing from the internal 

 vascular system into a single leaf or other external appendage, it will be 

 necessary to bear this in mind so as to distinguish those scars from another 

 character hereafter to be mentioned under the name of leaf- scars. The 

 distance of the series of vascular scars from each other longitudinally, 

 and on corresponding parts of different stems of Sigillaria, appears to 

 yary, at least this is the case with the three individuals under considera- 

 tion. On the one, in the Sunderland Athenaeum, they are much closer to 

 each other at the bottom than at the top, but on the specimen in the 

 Newcastle Museum, already described, they are nearly at equal distances 

 from each other (generally I of an inch), throughout its whole length. 

 The other Newcastle specimen offers some disparity in this respect ; at 

 the bottom, where it is very much wrinkled transversely, the vascular 

 scars are an inch and a quarter from each other ; from two to four feet 

 from the base there is only half an inch space between them ; and 

 on the remaining part of the stem, this space is increased to an inch. 

 This singular approximation of the vascular scars on the middle of the 

 stem, does not apear to arise from any downward pressure, for this part 

 shews no appearance of wrinkles, but, on the contrary, a perfectly smooth 

 surface. These evidences, and others hereafter to be adduced, incline 

 me to think that the stems of Sigillaria were subject to irregularities in 

 their longitudinal development. This last specimen affords another re- 

 markable character, the existence of which might be readily doubted, 

 were it not too obviously displayed ; on the lower part of the stem and 

 completely round it, the median line of the ribs is sunk below the level 

 of the furrows, so that the former are actually concave instead of being 

 convex.* As I intend hereafter to advert to the origin of this remark- 

 able character, any further allusion to it at present may be conveniently 

 deferred. 



Besides the vascular scars, the whole surface of the ribs in a great 

 many places is marked with longitudinal strice. In general these strice are 

 straight, but occasionally they are flexuose, especially where the ribs are 

 broad, and in this case they turn in towards the vascular scars. Lindley 

 and Button's figures of Sigillaria reniformis (PI. 57), and the so-called 

 Sigillaria Jlexuosa (PI. 205), afford a good illustration of both kinds. 



I shall now consider some other characters of Sigillaria, and for the 

 present waive any further particulars connected with the specimens 

 which have just occupied our attention. 



The most obvious features characteristic of the stems of this genus are 



* Vide Plate I, diagram 2, which shews the ribs a reduced to half the width of 

 the originals ; b indicates the fun'ows. 



