CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 93 



the leaf-scar are fine lines which cluster round the small puncti- 

 form cicatricule. 



In some species, such as SigiUaria rugosa, Brongt., SigiUaria 

 elongaia, Brongt., and SigiUaria Deutschi, Brongt., the ornamen- 

 tation forms a very distinct band extending from one leaf-scar 

 to the other, and thus divides the rib into three longitudinal 

 tracts, the two lateral being smooth and the central ornamented, 

 and bounded by the two lateral lines which descend from the 

 lateral angles of the leaf-scar. The ornamentation of the central 

 band consists of short transverse ridges or dots, or a mixture of 

 both. The markings are generally stronger immediately beneath 

 the leaf-scars, and become more faint as they reach the next 

 lower scar, shortly above which the}' generally assume a slightly 

 different arrangement. Modifications of this form of ornamenta- 

 tion occur. 



The cone-scars form verticils, sometimes of a single series of 

 sub-circular or oval cicatrices, as in SigiUaria elegans. In 

 SigiUaria tesseUata and other species the cone-scars form broad 

 verticils, the number of contiguous cone-scars placed in vertical 

 rows varying from three to twenty.^ The cone-scars are frequently 

 deformed from the pressure of the ribs, and at the same time 

 they generally cause a deformation of the leaf-scars in their 

 immediate neighbourhood. 



The remaining two sections — Clathraria and Leiodermaria — 

 are also most intimately connected. The conditions which gave 

 rise to these two groups have not only been found in the same 

 species, but on the same specimen, though some species seem 

 only to possess a Leiodermarian condition. 



Weiss was the first to point out that SigiUaria Brardii, 

 Brongt. (belonging to the Clathraria), passed by gradual transi- 

 tions into SigiUaria spinulosa, Germar (Leiodermaria Section), 

 and that this latter species was consequently only a condition of 

 the former.- 



Shortly afterwards M. Zeiller figured a specimen showing the 

 organic union of SigiUaria Brardii, Brongt., and SigiUaria 



1 Zeiller, Flore foss. Bassin houil. de Valenciennes, PL LXXXV. , figs. 

 1 and 5. 



'■^ Weias, Zeitsch. d. deut. geol. Gesiell, 1888, p. 566. 



