ON THE BRITISH FOSSIL CORALS. 101 
modifications in the faune, especially as regards the corals. The arenaceous 
limestones situated upon the coralliferous dolomitic limestones of the old 
Welsh reef contain a feeble coral assemblage, and present no evidence of the 
existence of coral reefs. A great number of Mollusca are found in the depo- 
sits ; some existed during the deposition of both, and others were limited in 
their range to one or the other ; but the bathymetrical changes gave the corals 
no chance, and doubtless the reef species died out, their ova finding no rest- 
ing place on that particular area. 
The zones which succeeded Ammonites Bucklandi appear to have been 
unfavourable to certain forms of corals, especially to those which collect 
together in vast tracts, forming varieties of reefs. The modern representa- 
tives of the species found in the Liassic strata above the zone of Ammonites 
angulatus indicate deep water (30 to 100 fathoms). Where the reefs of the 
period were is certainly not determinable. 
The corals of the Middle and Upper Lias are very rare. 
The corals contained in the Liassic strata of Britain, France, Germany, 
and Italy have a very decided community of facies; at the same time it is 
evident that some portions of the Liassic coral-fauna resemble Triassic types, 
and that another portion is allied to the Oolitic. 
This was to have been expected; for it is evident that the stunted Theco- 
smilie and the Astrocenie of the zone of Ammonites angulatus are the de- 
scendants of the equally stunted 7'hecosmiliw and Astrocaenie of the Triassic 
age. Moreover the descendants of the Jsastrew and of the larger Montl- 
valtice of the Lower and Middle Lias luxuriated in the Oolitic seas. The bulk, 
however, of the Liassic coral-fauna is characteristic of and special to the 
formation, and, as is the case in the other great series of strata, certain as- 
semblages of species appear to characterize certain definite horizons. Yet 
not unexceptionably ; for some species range into higher zones in certain 
areas, whilst others, which are confined to a definite horizon in one area, are 
found below and above the equivalents of the horizon in a distant locality. 
Thus a species which is only found in a particular bed, and is associated with 
a particular molluscan fauna in one locality, may be found associated with a 
molluscan fauna antecedent or subsequent in its recognized succession in 
‘ another place. 
The persistence of a species in a succession of deposits and its consecutive 
association with different groups of contemporaries and competitors is con- 
stantly observed in the Lias. 
The groups of Madreporaria have a general relation to certain zones of 
life and to certain strata, besides very definite relations to others. It is not 
probable that corals and Ammonites had any close biological relations, but 
only those of a general nature; but corals were certainly en rapport with 
certain molluscan genera, especially with lithodomous groups; so that when 
corals of the Lias are said to belong to such and such a zone of Ammonites, it 
is to serve the purpose of the artificial but very necessary classificatory system 
of geology. If the Madreporaria are associated with certain Ammonite zones, 
it must be understood that it is only an approximative classification, and that 
the Ammonites and the Madreporaria may range higher than their supposed 
restricted zone, or not even be represented in certain portions of its area. 
There are a few Triassic species in the Liassic coral-fauna, and the branch- 
ing corals of the Sutton stone have generally a Triassic facies. The majority 
of the corals of the Lower Liassic strata are peculiarized by the imperfection 
of the septal arrangement, and by their epithecate wall. It may, in fact, be 
asserted that the so-called ‘‘ rugose” characteristics of the greater part of the 
