250 SIGILLARIEAE. 



only Leiodermaria in which they are known 1 , and this is the effect of 

 lateral contact at every point owing to the peculiar character of the surface. 

 They are polygonal on the other hand and elongate, as far as is known, 

 in Rhytidolepis and Favularia. Sigillaria Brardii is the only species in the 

 group of Cancellatae in which scars of this kind have as yet been found ; 

 here according to Zeiller's 2 fine figure the scars are isodiametrically 

 polygonal, and if they are represented as circular in Renault 3 this may 

 very well be explained by the imperfectness of the figure. Williamson's 

 description cited above, which belongs according to Renault 4 to this 

 species, agrees essentially with that of Zeiller. The character of the 

 surface of the scar, which projects convexly in the mould, is quite different 

 to that of the leaf-scar. In its centre is a circular protuberant trace of 

 considerable dimensions, and the entire periphery is occupied by stout 

 sinuous radiating wrinkles, between which there are usually fragments of 

 coal still adhering. We should no doubt be able to see other details on 

 the surface of the rind of coal on the cast ; but though I have myself found 

 several good specimens of moulds, a well-preserved cast of the kind has not 

 yet fallen in my way. 



Authors have described a number of species of Sigillariae, all of which 

 are distinguished by the form and character of the leaf-cushions. The 

 method is very precarious, for we cannot say to what extent alterations 

 supervene with the growth of the plant. The scars of the fructification are 

 known as yet in very few forms, and yet distinctions have been already 

 observed in their distribution on the surface of the stem, and these seem to 

 supply characteristic marks. From this source we may expect to obtain 

 much help in arranging the group, as Zeiller 5 has very conclusively shown, 

 if we can once arrive at more extended knowledge through further research. 

 So far as we can venture to generalise from our present scanty knowledge, 

 the scars of the fructification are confined in Rhytidolepis and Favularia to 

 more or less broad intercalary zones, which form rings round the stem. 

 Within these zones the scars, touching one another above and below, form 

 vertical rows inserted between the ribs in Sigillaria tessellata 6 , in S. 

 Lalayana, Schimp. (Fig. 27), and in Sigillaria Lorvvayana 7 . In these 

 species they are nearly rectangular through mutual pressure. On the 

 determination of species by authors I do not venture to express an opinion ; 

 but I may call attention to the great resemblance between the two figures 

 first cited. The scars are developed in a broad transverse zone between 

 the ribs, and being everywhere isolated they are elliptical in form or two- 



1 Renault (2), vol. i, t. 17, f. a. Zeiller (1), t. 174, f. i. 3 Renault (2), vol. i, t. 17, f. i. 

 4 Renault (2), vol. iii, p. 9. 5 Zeiller (12). * Zeiller (1), t. 173, f. 2. 7 Dawson 



(12), p. 43 with figures. 



