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XXIII.—On the Internal Structure of Sigillaria elegans of Brongniart’s “ Histoire 
des végétaux fossiles.” By Robert Kidston, P.R.S.L. & E., F.G.S. (With 
Three Plates.) 
(MS. received February 23, 1905. Read May 1, 1905. Issued separately June 30, 1905.) 
INTRODUCTION. 
Before giving a description of the specimen which forms the subject of this 
communication, it seems desirable that a brief summary of the literature dealing with 
the internal structure of Srgillaria, and some general remarks on the classification of 
the genus, should be given. ; 
More for the purpose of convenience than on scientific grounds, the genus Srgillaria 
is usually divided into four groups. ‘These groups were originally supposed by their 
founders to be of generic value, but experience has shown that the characters on 
which they were founded are more or less common to all four divisions, and in some 
cases the distinctive divisional characters even occur on the same specimen. 
Group I. RHYTIDOLEPIS, Sternberg, 1823. 
Stem ribbed, furrows distinct, straight or slightly flexuous. Leaf scars more or less 
distant, as wide as, or narrower than, the rib. 
Group II. FAVULARIA, Sternberg, 1823. 
Stem ribbed, furrows flexuous. Leaf scars with prominent lateral angles, and 
occupying the whole width of the rib. The lateral angles project slightly, and, alter- 
nating with those of the neighbouring leaf scars, impart a zigzag course to the furrows. 
Group III. CLATHRARIA, Bronegniart, 1822. 
Stem without ribs. Leaf scars placed on contiguous rhomboidal, slightly elevated 
cushions, which are separated by deep oblique furrows. . 
Group IV. LEIODERMARIA, Goldenberg, 1857. 
Stem without ribs. Leaf scars distant and unprovided with cushions. 
Groups I. and II. pass into each other; and though in a few cases one can refer 
certain species to the Favularia section, such as Srgillaria elegans, there are others 
which so combine the characters of groups I. and II. that in practice it is impossible to 
treat them as members of distinct groups. 
TRANS. ROY. SOC. EDIN. VOL. XLI. PART III. (NO. 23). 80 
