58 MR ROBERT KIDSTON ON 



younger state of the plant than any of the other specimens. The leaf-cushions are 

 transversely rhomboidal, and the leaf-scar of a similar form occupies its upper portion. 

 There is no part of the cushion above the leaf-scar, and in this Sigillaria semipulvinata 

 differs from almost all the other species of the Sigillaria Brardii type. The lateral 

 angle of the leaf-scar meets the margin of the leaf-cushion about half-way between its 

 lateral angle and the apex of the cushion. The leaf-cushions are not strictly contiguous, 

 but are separated by a slight interval ; therefore, though the arrangement of the leaf- 

 cushions is clathrate, still, as they do not rest on each other as in the typical Clath- 

 raria* the species shows some relationship to the Leiodermaria section, where the leaf- 

 scars are more or less distant. 



PI. III. fig. 2. 



This shows an older form of the plant. The leaf-cushions are more distantly placed 

 here than in fig. 1. There is also seen in fig. 2 a somewhat irregular longitudinal split- 

 ting of the bark in lines following the direction of the upward rows of leaf-cushions. 

 This is evidently brought about by a Assuring of the bark caused by increase of the stem 

 in girth, and it gives a Favularia-like appearance to the specimen which is directly 

 derived from what was originally a Clathrate or Leiodermarian form. 



PI. III. fig. 3. 



This shows still more clearly the Favularia arrangement of the leaf- cushions, and 

 also illustrates the variations in their size. Two of the upper leaf-cushions and accom- 

 panying leaf-scars are given at fig. 3a x 2, and at 3& and 3c, natural size. Here the leaf- 

 cushion is not much larger than seen on figs. 1 and 2, but at the lower part of this fossil 

 (fig. 3) a considerable increase in the size of the leaf-cushion is observable (fig. 3c), in 

 which increase the leaf-scar also participates. Two rows of faint transverse lines are 

 present on the larger cushions (fig. 3a). 



PI. III. fig. 4. 



This is apparently from a somewhat aged specimen. The leaf-cushions are practically 

 contiguous, and show below the scar two rows of faint transverse lines (fig. 4a). The leaf- 

 cushion here is fully longer than broad. 



PI. III. fig. 5. 



This represents a similar condition to that shown at fig. 4. On the lower portion of 

 the fossil the leaf-cushions are contiguous ; on the upper part, more or less separated. 



The study of this species shows the caution that is necessary in bestowing names on 

 fragments of Sigillaria. If figs. 1 and 4 are compared, they look at first sight very 



* As the leaf - cushions appear to become more, distant with age, probably the younger conditions would 

 represent true CInlhraria. 



