178 Mr. R. Kidston on Ulodendron. 



these cushions more or less exceed in area the surface to 

 which the leaf is articulated, and have a casual resemblance 

 to the " field " in Lepidodendron, but with this they have no 

 real relation. In Lepidodendron the leaf-base is attached to 

 the "field" (c, fig. 15) as well as to the vascular scar; in 

 SigiUaria, on the other hand, it is only attached to the 

 vascular scar. 



I now hope to show that in Sigillaria discophora, Konig sp. 

 (= U. jnajus, L. & H., and U. minus, L.& H.), and Ulodendron 

 Taylori, Carruthers, the leaf- scar agrees in all essential points 

 with those of the Clathrarian Sigillarice, of which I have taken 

 Sigillaria Brardii, Brongniart, as the type. In fig. 12, PI. VII. 

 (specimen No. 12), a great diversity is seen in the form of 

 the leaf-scar. Immediately beneath the Ulodendroid scar 

 the leaf-scars are of the SigiUaria-Brardii type. These are 

 enlarged in fig. 12 a, PL YII. They are rhomboidal, their 

 upper and lower angles rounded, and their lateral angles pro- 

 duced and prominent ; the leaf-scars are also placed upon 

 slightly elevated cushions, and though the cushion is not 

 much larger than the vascular scar, its presence is clearly 

 observable. The small cushions on which the leaf-scars sit 

 are well seen in PI. V. fig. 8. This, I think, proves the 

 structural identity of the leaf-scar of Sigillaria discophora, 

 Konig, sp. (= Ulodendron majus, L. & H.), with that of the 

 Clathrarian group of the genus Sigillaria. 



I have not met with any specimens of Sigillaria discophora 

 which clearly show the vascular-bundle cicatricules ; but such 

 have been figured by Sir William Dawson under the name of 

 Lepidophloios parvus^, Avhere they are represented as of the 

 ordinary Sigillarian type, with three vascular-bundle " dots," 

 the central pimctiform and the two lateral lunate. At the part 

 marked h, fig. 12, PI. VII. (specimen No. 12), and enlarged 

 at fig. 12 5, the scars assume a quadrangular form and usually 

 show a central " dot." Fig. 13 a, PL VIL, gives a few leaf- 

 scars, natural size, from fig. 13 (specimen No. 14). This 

 form of leaf-scar, arising from the age of the specimen^ and 

 perhaps also from changes which have taken place during 

 mineralization, has given rise to Dawson's Lepidophloios 

 tetragonus f. The fact of this form of leaf-scar occurring on 

 the specimen represented in fig. 12, PL VII., along with the 

 ordinary leaf-scars of the species, proves conclusively the 

 identity of Lepidophloios tetragonus, Dawson, with Sigillaria 

 discophora, Konig, sp. On some specimens of this species, 

 especially the older and larger ones, the bark also becomes 



* Acadian Geol. 2ncl ed. p. 455, fig. 170 g3. 

 t L. c. p. 465, fig. 170 D. 



