228 Proceedings of the Royal Physical Society. 
The Calamariew are strongly represented, but contain few 
species peculiar to the series. The same remark may be 
made in connection with the genus Sphenophyllum. The 
Lepidodendra here hold about the same position in regard 
to species and their frequency of occurrence that they do 
in the Lower Coal-Measures, Lepidodendron ophiurus, 
Brongt., being also here the species most commonly met 
with. 
The genus Lepidophloios is not very common. Lepidophlotios 
laricinus, Sternb. sp., has only been found in this horizon in 
Britain, and it is rare. Lepidophloios acerosus, L. and H. sp., 
is, however, more frequent. 
In the Middle Coal-Measures the genus Sigillaria attains 
its maximum state of development, and is represented by 
many species, a number of which are peculiar to these rocks, 
and many of those which ovcur in other horizons are generally 
more plentiful here than elsewhere. Some of those which 
appear to be peculiar to the Middle Coal-Measures are Sig. 
polyploca, Boulay, Sig. elongata, Brongt., Sig. Deutschiana, 
Brongt., Sig. Saulii, Brongt., and Sig. cordigera, Zeiller. 
Cordaites is frequent. The most common species here, as in 
the Lower Coal-Measures, is Cordaites principalis, Germar sp. 
As far as our investigations have yet gone, the Middle 
Coal-Measures would appear to have possessed a richer flora 
than any of the other divisions of the Carboniferous forma- 
tion—certainly a richer flora than that occurring in the Lower 
Coal-Measures; but further investigations are necessary before 
final conclusions on this point are warranted. 
VI. TRANSITION SERIES. 
Typical Area—Lower Pennant Rocks of the South Wales 
Coal Field. : 
This series, as its name indicates, is particularised by an 
‘almost equal mixture of the species which are characteristic 
of the rocks on which it rests and of those which overlie it. 
So far as our work has gone, the only series in the Coal- 
Measures necessitating the use of the term “ 7ransition” 
met with, lies between the Middle and Upper Coal-Measures. 
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