214 A. C. Seivard — Variation in Sigillarim. 



preserved with tbeir cortical tissues entire, and those which have 

 been to a greater or less extent decorticated. 



Genera like Knorria, Aspidiaria, Bergeria, and others are now 

 generally recognized as imperfectly preserved Lepidodendoid stems. 



We propose to confine ourselves in the present instance to the 

 Sigillarics. As a general rule, for purposes of classification and 

 specific determination, we have to rely on certain external characters 

 of the stems or branches. Seeing bow the surface of a partially 

 decorticated stem differs in appearance from that of a stem with its 

 outermost cortical tissues preserved, one cannot be too careful in 

 selecting well-preserved specimens before venturing to make any 

 definite statements as to specific character. Mr. Kidston 1 lays special 

 stress on this point. He remarks : " When determining the various 

 species of the genera Lepidodendron and Sigillaria, unless the outer 

 surface of the bark is well preserved and exhibits the form and 

 arrangement of the leaf-scars, it is admitted that the plants do not 

 show the characters by which a specific, or even in some cases a 

 generic determination can be made." 



The Sigillarice may be divided into four sections or groups, 

 Bhytidolepis (Sternberg), Favularia (Sternberg), Clathraria (Brong- 

 niart), and Leiodermaria (Goldenberg) ; or a more convenient 

 classification is that adopted by M. Zeiller, 2 and others, where we 

 have only three sections, Bhytidolepis, Clathraria, and Leiodermaria. 



Such a classification as this, although convenient, is necessarily 

 unsatisfactory, and one must expect from time to time evidence to 

 be forthcoming which tends to break down the artificial barriers 

 or fill up supposed gaps between the representatives of the several 

 sections. 



Some striking examples have recently been brought forward by 

 Herr Weiss, of Berlin, and M. Zeiller, of Paris, of connecting links 

 between two of these sections. 



It may not be without interest to give a short resume of the three 

 papers in which proofs are given of the gradual passage from a type 

 figured by Solms-Laubach 3 as representative of one section, Leioder- 

 maria, to one quoted by him as an example of another section, 

 Clathraria. 



In the "Zeitschrift der Deutschen Geologischen Gesellschaft," 

 for 1888, p. 565, there appeared a short notice by Weiss, " Ueber 

 neue Funde von Sigillarien in der Wettiner Steinhohlengrube." In 

 this paper he deals especially with specimens of Sigillaria recently 

 found in the Coal-measures of the Wettin district, Sigillaria spiuu- 

 losa (Germar), belonging to section Leiodermaria, and S. Brardi 

 (Brongniart), one of the Clathraria (Cancellated, Weiss). To quote 

 Weiss's words — " Of exceptional interest is a large series of speci- 

 mens which, beginning with S. spinulosa, gradually passes, almost 

 without a break, into S. Brardi. In this case there is no recogniz- 

 able division between Leiodermariee and Cancellated, indeed it is 



1 Ann. and Mag. Nat. Hist. vol. xvi. 5th series, p. 123. 



2 Flore fossile du bassin houiller de Valenciennes, p. 512. 



3 Eiuleitung in die Palaopkytologie, p. 249. 



