24 2 SIGILLARIEA E. 



Heimbach near Commern in the Eifel, and this is not altogether above 

 suspicion, though Weiss * too has recently pronounced in favour of its 

 belonging to Sigillaria. The form in question, Sigillaria oculina 2 , is in fact 

 very like those, of the group Leiodermaria, and this is exactly the dominant 

 group in the most recent of the deposits which contain any Sigillariae. 



Turning to the consideration of the impressions and casts of stems, 

 we find it scarcely possible to give a general account of them, because the 

 groups of species, the genera if we choose so to call them, differ so greatly 

 from one another. The old genus Sigillaria separates after removal of the 

 Megaphytae which were placed in it by earlier authors, Brongniart 3 for 

 example, into the divisions or genera, Rhytidolepis, Clathraria, Favularia 

 and Leiodermaria. The most peculiar form and the one which departs 

 most widely from the habit of Lepidodendreae is Rhytidolepis, and it may 

 therefore be placed first in the list. Here the entire surface of the stem is 

 formed of peculiar broad vertical ribs, which bear the leaf-scars on their 

 flatly convex dorsal surface, and are separated from one another by shallow 

 but acute-angled furrows. The arrangement of the leaves has been speci- 

 ally studied by Goldenberg 4 and Stur 5 . The latter seeks to prove that 

 the longitudinal ribs do not correspond to the orthostichies, but represent a 

 system of parastichies which by a peculiar displacement has passed into a 

 vertical position. In that case we should not have, as appears at first sight, 

 a succession of somewhat irregular many-leaved alternating whorls, but the 

 relative positions of the leaves would be as in Lepidodendron, only altered 

 by displacement, and with a divergence which was determined in one case 

 to be i/gV Stur's publication will give further information on this point ; 

 here we will add only that he also occasionally found a distinct appear- 

 ance of orthostichies in Lepidodendron, and that he refers this also to one 

 of the steep oblique line-systems and explains it by displacement. Lepi- 

 dodendron costatum is a similar impression 7 . Various other irregularities 

 occur in the position of the leaves, and are not unconnected with the fact 

 that new ribs, ending blindly below, suddenly and not unfrequently make 

 their appearance between the old ones in stems of Sigillariae 8 . 



The longitudinal ribs of the stem of Rhytidolepis originate in the 

 coalescence of the leaf-cushions which stand vertically one above another. 

 When the coalescence is very perfect, the scars of the laminae of the leaves 

 lie at regular distances on the smooth uniformly convex surface of the ribs, 

 and the separating furrows are simply straight lines (Fig. 26 A}. In proof 

 of this we may point to Sigillaria Voltzii in the long list of Brongniart's 9 

 figures. But an indication of the separate leaf-cushions which have united 



1 Weiss (9). 2 Blanckenhorn (1), p. 132 ; t. 20, f. 9. 3 Brongniart (1). ' Goldenberg (1). 

 5 Stnr (5), p. 293. 6 Stur (5), t. 23, f. 2. 7 Lesquereux (3), vol. ii, t. 44, f. 7. " Weiss 



(1), t. 15, ff. I, 2. 9 Brongniart (1), vol. i, t. 144, f. I. 



