vaugha^j : a note on carboniferous sequence. 81 
(1) (Uppermost Avonian). 
A typical fauna may be classified as follows : — 
Specialised, decadent, and reverted forms : 
Productus longispinus. 
Zaphrentis aff. Enniskilleni and Zaphrenti-AmplexiLS. 
Psevdamplexits, Beaumontia, cf. Favosites. 
Peculiar forms : 
Cyathaxonia rushiana, Cladochonus and Beaumontia. 
Abundant forms : 
Martinia glabra, Spirifer bisvlcatiis, Productus corru- 
gatus, and Orthids (all of which usually exhibit 
moribund characters). 
ChsiophyUids and Productus ' giganteu^ ' are rare. 
It is well known that this fauna does actually characterise 
the highest beds of the Avonian in several areas, but, since the 
lithological character of the beds in which this fauna occurs 
is always a pecuKar one, it is not, as yet, certain to what extent 
the fossil-assemblage is a function of its environment. In 
other words, we do not know that the same environment, during 
time, was not characterised by a very similar fauna. It 
seems most probable indeed that time-variation has been, at 
least, exaggerated by the variation consequent on change of 
environment. 
(2) The Posidonomya Becheri Beds (Lower Pendleside). 
The shales which are crowded with Posidonomya Becheri 
unquestionably indicate very definite conditions of depth and 
deposit ; it follows, therefore, that the sudden appearance of 
Posidonomya Becheri merely indicates a change of conditions, 
and by no means imphes that the Pendleside fauna is the lineal 
descendant of the or faunas. 
It is, as yet, unknown to me at what time P. Becheri made 
its first entrance, for I know of no deposits, during time, 
which indicate an environment or bathymetric level identical 
with that of the P. Becheri Beds. It seems, however, probable 
that the Cyatlmxonia and P. Becheri faunas were, at least in 
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