186 
G. W. Lee — Trepostomata. 
instability (e.g. Tabulipora scotica and T. sparsitabulatd). Another striking feature of 
the British fauna is the presence of singular species apparently unconnected with the 
other members of the group ; for instance Koninckopora inflata and Tabulipora debilis. 
All these facts, namely the narrow vertical range, the often circumscribed horizontal 
distribution and the absence of visible links between the greater number of the species, 
seem to point to the influence of physical causes—not necessarily shown by the nature of 
the sediment—having favoured from time to time the immigration of the various types 
from some outside area. But the very complexity of our fauna precludes the possibility 
of offering suggestions as to the probable situation of its centre of dispersion. Com¬ 
parisons with the Lower Carboniferous trepostomatous faunas of continental Europe 
cannot yet be attempted, in some cases owing to the fact that Trepostomata are not repre¬ 
sented, in others on account of incomplete knowledge. On the other hand the North 
American fauna is very well known, and is the only one with which comparisons can be 
made. The relationship of the British and North American faunas lies in the presence of 
Leioclema , Batostomella and Dyscritella , and of the species of Tabulipora with centrally 
perforated tabulae [ Tabulipora , Section A = Stenopora Auctt.], all of which genera are 
represented in these two countries by more or less closely comparable species. But the 
resemblance ceases here. Stenopora (as restricted), the numerous species falling under 
Section B of Tabulipora and the “ Monticulipora inflata ,” have no equivalents in North 
America. 
From the fact that besides the species classed here as Stenopora , the genus Stenopora 
Lonsdale [non Auctt.] exists only in the Upper Palaezoic deposits of Australia and India 
(? Russia), one of two conclusions can be drawn : the British forms are either true 
Stenoporae, in which case the genus originated in the Atlantic area and then migrated 
eastwards, or they are but homoeomorphs of the Australian species. 
The purely theoretical points discussed above do not in the least detract from the real 
value which it is hoped the Trepostomata will be shown to possess as indices in correlating 
beds over considerable areas, when more becomes known of the occurrence of many of the 
species which at present are recorded from single localities only. Although many of the 
species, owing to their restricted occurrence—so far as the materials examined go—cannot 
yet be proved to be useful, it will be admitted that the numerous locality-records of 
others show them to be trustworthy indices in certain areas. For instance, Stenopora 
redesdalensis and Tabulipora howsei are common in Northumberland, Cumberland and 
the South of Scotland in beds of I) 1 age approximately. T. scotica and T. youngi , 
common in Central Scotland, have not been observed from beds older than the top of the 
