918 MR A. C. SEWARD AND MR A. W. HILL ON THE 



occasionally interrupted by the occurrence of an elongated elliptical group of parenchyma, 

 with the cells slightly extended in a radial direction. One of these groups is shown in 

 PI. I. fig. 8 ; the cells vary considerably in size and shape, the central region consisting 

 of smaller elements ; the group shown in the photograph is about 3 mm. in length, and 

 there is a second similar parenchymatous mass slightly above and to one side of the 

 group shown in the figure. These parenchymatous masses agree in their structural 

 features with the parenchyma accompanying the leaf-trace shown in PI. II. fig. 14 pr, 

 and it is probable that the more external groups like that of fig. 8 are the arms of the 

 parichnos which have been shown by Williamson * and others to bifurcate in the more 

 external region of the cortex in Lepidodendroid stems. In younger stems the two 

 arms of a parichnos would appear on the same level as seen in a tangential section of 

 the outermost cortex, and between them would be found the leaf-trace bundle ; in the 

 present instance we are dealing with an old trunk from which the leaves had fallen, and 

 the parichnos arms alone persist, the vascular tissue having been gradually crushed and 

 obliterated. It is well known that in the lower portions of large casts of Sigillarian 

 stems the two large elliptical parichnos scars are often seen to lose their regular paired 

 arrangement ; one may occur at a higher level than the others, or they may appear as 

 separate areas with no definite order, f 



B. Affinities of the Dalmeny Plant. 



In the foregoing description no reference has been made to the relationship of the 

 stem to other Lepidodendrese. The size of the stem and its anatomical characteristics 

 at once suggest a comparison with the famous Arran species described by Williamson 

 and others. We have no doubt as to the specific identity of the Dalmeny and Arran 

 trees ; an examination of the series of sections of the Arran plant in the Williamson 

 Collection (British Museum) reveals an identity in structural features. The Dalmeny 

 specimen is, however, much more perfectly preserved, and enables us to considerably 

 extend the diagnosis of the species. 



The fossil trees of Arran were discovered by Mr Wunsch;}; in volcanic beds of 

 Calciferous sandstone age at Laggan Bay, and briefly described by him in 1867. He 

 refers to the large stems as apparently Sigillarian, containing five or six " internal 

 piths " ; the smaller branches he identifies with Sigillaria, Halonia, and Lepidodendron. 

 Carruthers § afterwards visited the locality and gave a short account of the fossil 

 stems ; he speaks of having traced the radiating branches of a Stigmaria to a large 

 trunk of Sigillaria, and describes the internal " piths " of Wunsch as young stems which 

 had grown from spores carried into the hollow trunk of a large tree. Carruthers || 

 proposed the name Lepidodendron Wiinschianum in 1869 for a species from Arran in 



* Williamson (93), pis. iii. and iv. 



t Renault (96), p. 770. Vide also Renault and Roche (97), p. 17, where this point is referred to in the descrip- 

 tion of a silicified Syringodendron stem. 



% Wunsch (67), p. 97. Vide also Lyell (78), p. 547, and Seward (98), p. 89. 

 § Carruthers (69), p. 178. || Ibid. (69), p. 6. 



