PTERIDOPHYTA. 



I 521 



be Sigillarian ; Sir W. Dawson has, however, identified Ulodendron 

 with the next genus. Lepidophleeus (Lomatophlmis), which appears 

 to be exclusively Carboniferous, has the leaf-scars transversely elon- 

 gated, with three vascular points, and placed on distinct promi- 

 nences ; while the branches are thick, the leaves very long, and the 

 cones always lateral. Hallonia is founded on fruiting branches of 

 this genus ; while fruits of one type of the so-called Lepidostrobus 

 (fig. 1388) have been found attached to stems with the scars of 

 Lepidophlonis. Cy do stigma and Lepto- 

 phlceum are exclusively Devonian ; the 

 former being characterised by the circu- 

 lar or horse-shoe-like leaf-scars, and the 

 latter by the flat and rhombic leaf-bases 

 and obsolete scars. Leptophlceum occurs 

 in the United States and Australia. 



The existing genus Isoetes, the sole re- 

 presentative of the Isoetece, is known in 

 a fossil condition by two species from 

 the Miocene of the Continent, and by a 

 third from the Eocene of Colorado. 



With regard to the serial position of 

 the second great Palaeozoic family of the 

 Sigillarece, there has been much discus- 

 sion, but the general consensus of opinion 

 seems now to be in favour of placing 

 them in the present order ; although it 

 is quite probable that, as Sir J. W. Daw- 

 son suggests, at least some of them may 

 be more or less closely allied to the 

 primitive Gymnosperms. Their resem- 

 blance to the Lepidodendrece is indicated 

 by their strongly-marked external simi- 

 larity ; which is especially shown in the 

 tall, slender, and dichotomously-branch- 

 ing stem (fig. 1389), the slender grass- 

 like leaves, the leaf-scars arranged in 

 whorls, and the Stigmarian roots. These 

 trees, constituting the genus Sigillaria, 

 are mainly of Carboniferous age, and are 

 common to the Old and New Worlds; they attained very large dimen- 

 sions, their stems being sometimes as much as five feet in diameter. 

 Not unfrequently these stems are found in an erect position (fig. 

 1390), passing through several layers of rock ; while in other cases 

 they have been found attached to the Stigmarian roots which pene- 

 trate the clays underlying the seams of workable coal. The columnar 



Fig. 1389. — A, Reduced restora- 

 tion of Sigillaria Broivni; B, Do. 

 of 6". tessellata; from the Carbon- 

 iferous. (After Dawson.) 



