Benson.—Mazo carp on or the Structural Sigilla riostrobu s . 587 
recent contribution 1 to the anatomy of Isoetes does not essentially affect the 
problem. With reference to the relationship of Sigillaria to the other 
Lepidodendreae it might be useful to point out that the anatomy of the 
cone of Mazocarpon tends to prevent any great phylogenetic significance 
being attached to the presence of a double leaf-trace in some species of 
Sigillaria. Mazocarpon has but a single trace in its cone-scale, although 
there can be but little doubt that some of the Shore specimens belonged to 
Sigillaria mamillaris , as that is the species which was prevalent in the 
Shore balls yielding the bulk of the material, and S', mamillaris is one of 
the two species of Sigillaria in which the double leaf-trace has been 
identified. It is a well-recognized fact in morphology that the cone-scale is 
likely to retain ancestral characters longer than the foliage leaf, so that the 
division of the leaf-trace may be regarded as a recent character. 
Again, we may ask if the more detailed knowledge of the sporangia 
throws any new light on the interrelationships of the genera of Lepido- 
dendraceae. It has contributed to the removal of the view that was held 
by some botanists 2 that the sporange of Sigillaria had relatively lessr adial 
extension than that of Lepidodendron. Bearing in mind the distal extension 
of the sporange and the large mass of sporogenous tissue which is only 
partially fertile, we find no grounds for rejecting the very cogent theory that 
Sigillaria was an offshoot from some early Lepidodendroid stock. Though 
comparatively rare in the Lower Carboniferous rocks, a relatively unspecial¬ 
ized type of Mazocarpon ( M . Pettycurense) was already evolved, and with 
very little change the type persists to the Upper Coal Measures, where it is 
recognizable as incrustations. It is increasingly probable that it survived 
as Pleuromoia in the Mesozoic and as Isoetes to the present day. 
c. General Conclusion. 
In conclusion we may point out that when Zeiller made his discovery 
of the characteristic leaf-scars in vertical series on the peduncle of Sigillario- 
strobus Tiegkemii , in 1884, he really laid the foundation for the diagnosis of 
Mazocarpon as Sigillaria. As Dr. Scott says : 3 ‘ This correlation having 
once been effected it became possible to identify various other specimens as 
cogeneric, and the genus Sigillariostrobus now includes several species/ 
Among these species, those of the structural remains, Mazocarpon , as now 
described, may well claim a place. Moreover, if we take into account that 
we can trace Mazocarpon from the Coal Measures back to a period when 
Sigillaria was comparatively rare it is even probable that it is the character¬ 
istic type of sporangial fructification of the whole genus. 
1 Lang: Studies in the Morphology of Isoetes , I and II. Mem. and Proc. of the Manchester 
Lit. and Phil. Soc., vol. lix, Part II, 1915. 
2 Lady Isabel Browne: N. Ph., vi, pp. 153-6. 
3 Scott: Studies in Fossil Botany, p. 232. 
Q q 
