94 



TRANSACTIONS, NATURAL HISTORY SOCIETY OP GLASGOW. 



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

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



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

 Weiss and Dr. T. Sterzel,' on the Clathrate and Leiodermarian 

 Sigillariifi. 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.,'* 

 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.^ 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 spinulosa, 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 tliis 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 

 reni/ormis, Brongt.,^ from Hampstead Colliery, Great Barr, 



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

 XIV., fig. 1. 18S9. 



2 Hist. d. vegit.foss., p. 425, PI. CLVII., fig. 4. 



' "Die Sigillarien der preuss. Steink. u. Rotlil. Gebiete. II. Die 

 Oruppe der sub-Sigillarieu." — Ahhandl. d. Konig Preuss. G6ol. Landes- 

 an-slalt. Neue Folge, Heft. 2, Berlin, 1893, pp. i.-xvi. and 1-225, with 

 atlas of xxviii. plates. 



* Die fosfs. Fcora d. permischcn Formation, p. 200, PI. XXXIV., fig. 1. 



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



« Tram. Roy. Sec. Edin., Vol. XXXV., Part 5, p. 327, PI. I., fig. 11. 

 1888. 



