SIGILLARIEAE, 245 



of flat transversal furrows running above the scars. If these furrows become 

 deeper and more distinctly marked, and the scars are at the same time more 

 crowded together on the rib, then each cushion projects more decidedly 

 beyond the dorsal surface of the rib, and we have the character of Favu- 

 laria (Fig. 26 B\ the type of which is seen in Sigillaria elegans * and S. 

 tessellata 2 . In these forms the sharply polygonal leaf-scars, raised on con- 

 spicuous cushions above the common projecting rib which bears them, are 

 crowded together till they touch one another ; they alternate in the adja- 

 cent rows, and as they occupy the entire breadth of the rib their lateral 

 angles are thrust a little in between one another, and the bounding furrows 

 are slightly bent into a zigzag line. Species, in which the transversely 

 separated cushions are somewhat farther removed from one another, are 

 intermediate between Rhytidolepis and Favularia ; such are Sigillaria 

 Dournaisii 3 and S. Knorrii 4 . Lastly the transversal separation of the 

 cushions may go so far, that the rib on which they are placed disappears or 

 becomes quite inconspicuous, and then we have the Clathrariae (Fig. 26 C) 

 or, as Weiss names them, the cancellate Sigillariae. If even in Favularia 

 two systems of parastichies are distinctly apparent by the side of the 

 orthostichy, this is still more decidedly the case in Cancellatae. In addi- 

 tion to this a considerable increase in breadth takes place in the transverse 

 direction in the cushions of Cancellated ; they become rhombic in form and 

 thrust themselves laterally with their acute angles in between their neigh- 

 bours, so that the parastichies are sometimes more distinctly apparent than 

 the orthostichies. There may then be great resemblance in habit to Lepido- 

 phloios, with which genus, as has been already mentioned, these forms have 

 often been confounded ; but the size of the leaf-scar and the equal growth 

 of the cushion in every part make it easy as a rule to distinguish them if 

 carefully examined from Lepidophloios, in which the upper facets of the 

 cushion are excessively developed. The following figures of typical 

 Clathrariae may be cited : Sigillaria Defrancei 5 , S. Brardii 6 , and S. 

 Menardi 7 . 



While Rhytidolepis, Clathraria and Favularia are linked together 

 by intermediate forms, this cannot be said of Leiodermariae (Fig. 26 D), 

 in which the leaf-cushions as such are entirely wanting, and the leaf-scars 

 are set on the perfectly level surface of the rind and at wide distances from 

 one another. From among the figures of this group may be mentioned 

 Brongniart's Sigillaria leioderma, S. obliqua and S. venosa 8 , also S. lepido- 

 dendrifolia 9 and S. spinulosa 10 . The finest representation of a form of 



1 Brongniart (1), vol. i, t. 146, f. i. 9 Brongniart (1), vol. i, t. 156, f. i. s Brongniart 



(1), t. 153, f. 5 ; Goldenberg (1), t. 7. * Brongniart (1), t. 156, ff. i, 2. 8 Brongniart 



(1), vol. i, t. 159, f. i. 6 Brongniart (1), t. 158, f. 4; Germar (1), t. n, ff. i, 2 ; Goldenberg 



(1), t. 7; Weiss (1), t. 16. ' Brongniart (1), t. 158, ff. 5, 6. 8 Brongniart (1), t. 157. 



9 Brongniart (1), t. 161. 10 Renault (8), t. i, ff. 2, 3. 



