558 Palaeontologie. 



external characters of the fossil point more strongly to its be- 

 longing to Sigillaria discophora (= Ulodendion minus) than 

 to Lepidophloios, and further, that its internal structure, though 

 of the same type, is not identical with that of Lepidophloios 

 fuliglnosiis of Wiiliamson. 



In the specimen described here, the external surface ex- 

 hibits a single row of leaf-scars, the rest of the fossil being 

 somewhat decorticated. A transverse section shows a complete 

 Zone of the outer cortex with twenty-eight ribs, and a stele 

 with a perfectly continuous ring of primary wood, which is 

 surrounded by a zone of secondary wood. The pith has been 

 entirely destroyed, The outer margin of the primary v/ood is 

 deeply and regularly undulate or crenate, so as to form a 

 number of blunt ridges alternating with as many intervening 

 furrows. The inner margin of the xylem ring is very uneven, 

 sending irregulär toothed projections into the now empty pith- 

 cavity. The whole of the primary xylem, both protoxylem and 

 metaxylem, consists of scalariform tracheides, and no spiral or 

 annular elements occur. The outer margin of the secondary 

 xylem is also crenulated, but not so markedly as the inner 

 margin. The meduUary rays are usually one cell wide, and 

 their walls sometimes bear delicate scalariform thickenings. 

 The leaf-traces arise invariably at the base of the furrows of 

 the primary xylem, and no secondary thickening has been found 

 in them. The course oi the leaf traces is similar to that in 

 Sigillarla Menardl. 



The Author concludes that the stem of Slglllaria elegans 

 Brong. is very similar in structure to that of vS. elongata, the 

 only ribbed Sigillarla showing structure which has hitherto 

 been described. The corcna of the primary wood has more 

 rounded teeth in the former species, and the leaf traces also 

 appear to differ somewhat in their mode of origin. He also 

 States that the isolated Strand type of primary wood, known to 

 occur in some Siglllarias, is not a character of special impor- 

 tance, since it may pass, in the same specimen, into the type 

 with a continuous ring of primary wood. He contrasts the 

 structure of a ribbed Sigillarla with that of a Lepidophloios, 

 in which the primary wood also possesses a Corona, which 

 however is less prominent than in Sigillarla. He concludes 

 that the difference between these two stems is, in this respect, 

 only one of degree. He finds that in the Carbonlferous Lyco- 

 podlaceae there is a continuous chain of structural Variation in 

 the arrangement of the protoxylem elements, which binds clo- 

 sely together all the genera of Carboniferous Arborescent Ly- 

 copods. Between no two genera is there any outstanding 

 character in the structure of the vascular cylinder which sharply 

 separates them from each other. He is inclined to regard the 

 Aborescent Lycopods as a group which has left no descendants 

 except in the case of Sigillarla, the structure of whose cone 

 shows some similarity to the fructification of Isoetes. 



