236 Proceedings of the Royal Physical Society. 
lower portion of the same specimen is described by them as 
Sigillaria mutans, forma Lardinensis Brardii, Sterzel It 
may be convenient to distinguish some of the chief forms, 
especially when unattached to typical examples of Sigillaria 
Brardw, by such varietal terms as forma spinulosa, forma 
denudata, etc., but the fewer of such distinctive appellations, 
the less likely will there be misapprehension as to the value 
of such names. Students of fossil botany must acquaint 
themselves with the variations occurring in this plant both 
in regard to the presence or absence of cushions to the 
leaf-scars, and in their disposition on the stem; but to 
distinguish the innumerable forms occurring in Sigillaria 
Brardw by distinctive names can only overload an already 
too much burdened synonymy. Very few examples of 
Sigillaria Brardw are similar, though they are specifically 
identical. I therefore place Sigillaria mutans, Weiss, with 
its numerous named forms and varieties, among the synonymy 
of Sigillaria Brardii, Brongt. 
Under their Sigdlaria mutans, Weiss and Sterzel describe 
and figure a great number of forms and varieties, and it is 
clearly shown that*many of the Leiodermarian and Clath- 
rarian Sigillarie are only different conditions of the same 
plant. It does not, however, follow that all the Szgzlarie 
which have been placed in the Lezodermariw group merely 
represent certain states of Clathrate species, for, as far as one 
can see at present, such Leiodermarian species as Sigillaria 
camptotenia, Wood sp., are essentially distinct from those of 
the other groups. 
Weiss suggests that the Leiodermarian forms of Sigillaria 
Brardu (S. spinulosa, S. denudata, etc.) may represent the 
older condition of the plant,—a condition brought about by 
the increase in girth of the stem and its enveloping bark, 
which causes the leaf-scars to be drawn apart, and the 
prominence of the cushion effaced. In some cases this may 
explain the formation of Leiodermarian conditions, but it is 
certainly not the cause of all. In the specimen I give on 
Plate VII, Fig. 1, from Staffordshire, the Sigillaria denudata 
portion is immediately followed by the Sigillaria Brardi part. 
T2B00s its, pp. LUO; ASG: 
