94 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



spinulosa, Germar. 1 It was also shown that Sigillaria rhom- 

 boidea, Brongt., 2 only represented an intermediate state. 



In 1893 appeared a most elaborate memoir, by the late Dr. 

 Weiss and Dr. T. Sterzel, 3 on the Clathrate and Leiodermarian 

 Sigillaria?. Here are most admirably figured and described many 

 forms of Sigillaria Brardii, including conditions which were at 

 one time supposed to represent distinct species. 



A very interesting specimen (No. 818), showing the organic 

 union of Sigillaria Brardii, Brongt., Sigillaria denudata, Gopp., 4 

 and Sigillaria rhomboidea, Brongt., from a railway cutting, 

 Florence Colliery, Longton, North Staffordshire, which was 

 collected by Mr. F. Barke, was figured by myself in 1896. 5 In 

 the Sigillaria Brardii form the leaf -scars are placed on slightly- 

 elevated cushions, but in the Sigillaria denudata state the leaf- 

 cushions are entirely effaced. 



Weiss has suggested that the Leiodermarian forms of Sigillaria 

 Brardii (Sigillaria spimdosa, Sigillaria denudata, <kc.) may 

 represent an older condition of the plant — a condition brought 

 about by the increase in the girth of the stem, which has caused 

 the leaf-scars to be drawn apart and the leaf-cushions to be 

 effaced. In some cases this may probably explain the occurrence 

 of the Leiodermarian condition, but at other times it may have 

 been caused by a period of more rapid growth. 



But it must be noted that the approximation and separation 

 of the leaf-scars is not restricted to the Clathraria-Leiodermaria 

 Sections of Sigillaria. The same phenomenon occurs in the 

 Rhytidolepis Section. I have figured a specimen of Sigillaria 

 reniformis, Brongt., 6 from Hampstead Colliery, Great Barr, 



1 Zeiller, Bull. Soc. Geol. d. France, Ser. 3, Vol. XVII., p. 603, PI. 

 XIV., fig. 1. 1889. 



2 Hist. d. veget.foss., p. 425, PI. CLVIL, fig. 4. 



3 "Die Sigillarien der preuss. Steink. u. Rothl. Gebiete. II. Die 

 Gruppe der sub-Sigillarien." — Abhandl. d. Konig Preuss. G6ol. Landes- 

 anstalt. Neue Folge, Heft. 2, Berlin, 1S93, pp. i.-xvi. and 1-225, with 

 atlas of xxviii. plates. 



4 Die foss. Flora d. permischen Formation, p. 200, PI. XXXIV., fig, 1. 



5 Proc. Roy. Phys. Soc. Edin., Vol. XIII., p. 233, PI. VII., fig. 1. 



(! Trans. Roy. Sec. Edin., Vol. XXXV., Part 5, p. 327, PI. I., fig. 11. 

 1888. 



