216 A. C. Seward — Variation in Sigillaria?. 



It is known that Favularia and Rhytidolepis pass into Can cell at a and 

 Favidarice; that Leiodermarice pass into Clathrarice has already been 

 shown. One may quote here, as hearing on the remarks of Weiss, 

 a sentence from Solms-Laubach, 1 "Whilst Rhytidolepis, Clathraria, 

 and Favidaria are connected with one another by intermediate forms, 

 the same cannot be said of the Leiodermarice, in which the leaf- 

 cushions, as such, are entirely wanting, and on whose perfectly 

 smooth cortical surface the leaf-scars are situated at a considerable 

 distance from one another." In the " Bulletin de la Societe 

 geologique de France," 2 M. Zeiller publishes some interesting notes, 

 " Sur les Valuations de formes du Sigillaria JBrardi, Brongniart," 

 in which he begins by referring to the attempt made by Boulay 3 

 to reduce the unnecessarily large number of species of Sigillaria. 

 Zeiller 4 himself has pointed out certain differences which should be 

 referred to differences in growth, and are not such as to justify the 

 separation of distinct species. 



A photograph is given by Zeiller of a specimen of Sigillaria 

 showing perfectly clearly that Leiodermarian and Clathrarian types 

 pass into one another. In the upper part of this specimen the leaf- 

 scars are very prominent, broader than high, and separated by well- 

 marked grooves, in fact we have here the characters of S. Brardi. 

 Towards the lower end of the specimen the grooves gradually dis- 

 appear and the leaf-scars get farther apart, the cushions become less 

 and less distinct and the surface becomes even, having the charac- 

 teristic wrinkling ornamentation. Still further towards the lower 

 end the leaf-scars tend to come together again. The middle part of 

 the specimen corresponds very closely, except in having no root (?) 

 scars, with S. spinulosa. " S. spinidosa is then only a condition of 

 S. Brardi, corresponding to a more rapid elongation of the stem or 

 branches." By examining very carefully the S. spinulosa part of the 

 specimen, a slight indication can be detected of the leaf-cushions, 

 which become gradually more pronounced, until we have finally 

 S. Brardi. In other parts the surface of the stem is perfectly even, 

 and no traces of leaf- cushions can be seen. M. Zeiller points out 

 that, in spite of these variations, there are certain features which 

 remain constant ; the form of the leaf-scars, the relative position of 

 the cicatriculse on the leaf-scars, and the mode of ornamentation of 

 the bark. M. Zeiller 5 has previously given what he considers the 

 most constant characters on which to rely in the determination of 

 species. In the present paper reference is made by Zeiller to a 

 specimen of S. spinidosa described by Benault showing leaf-scars 

 on the fruit-bearing branches corresponding in shape and position 

 to those of S. Brardi. 



Attention is called to the fact that although such apparently 

 different types as S. spinulosa and S. Brardi have been shown to be 



1 he. tit. p. 251. 



2 3e ser. t. 17 (1889), p. 603. 



3 Le terrain houiller du Nord de la France, p. 47. 



4 Flore foss. du bassin houiller de Valencienues, p. 513. 

 6 Ibid. p. 513. 



