76 Mr J. EB. Marr, On Homotaais. [Feb. 14, 
Dimorphograptus in Britain, Thuringia, Scandinavia. 
Rastrites — Britain, Thuringia, Bohemia, Scandinavia. 
Cyrtograptus — Britain, Bohemia, Scandinavia. 
It will be seen that the order of succession is constant. 
Nowhere do we meet with Cyrtograptus in beds below those 
containing Rastrites, and nowhere with beds containing Rastrites 
below those with Dimorphograptus, and similarly with the other 
forms. 
Again, not only is the order of appearance identical, but in 
many cases, if not in all, that of disappearance of the forms 
mentioned, and whether this be the case or not, the genera dis- 
appear in different places at a time when those places were marked 
by the occupation of similar faunas. For instance, Rastrites dis- 
appears at the period when the areas in which it is found were 
occupied by a fauna which Prof. Lapworth has described as the 
Gala fauna. 
The major subdivisions I have marked out by the occurrence 
in each of one dominant form, can be split up into a series of 
zones, each of which has a characteristic assemblage grouped 
around one dominant form. To illustrate this, I will quote one 
instance, that of the correspondence of the zones of the Birkhill 
shales of the south of Scotland, as worked out by Professor Lap- 
worth, with those of the similar beds of the south of Sweden, 
described by the late Dr Tullberg. The zones are as follows, in 
ascending order: 
S. Scotland. S. Scandinavia (Scania). 
Zone of Diplograptus acuminatus = Zone of Diplograptus, n. sp. 
Diplograptus vesiculosus = —— Monograptus cyphus 
Monograptus gregarius 
Monograptus convolutus 
Foncsor je eeed cometa \— Teg’ (an co- 
onograptus spinigerus meta 
Zone of Rastrites maximus = Zone of Monograptus turriculatus. 
The thickness of the whole of the Birkhill shales is only about 
140 ft., that of the corresponding Rastrites beds of Scania about 
400 feet. Comparing these zones in greater detail, we find that 
(i) the lowest zone in Sweden (which is placed by Dr Tullberg with 
the group below the Rastrites beds), is marked by the absence of 
Monograptus, which first appears in the next succeeding zone, and 
by the presence, along with the dominant form, of Climacograptus 
scalaris, which passes up into succeeding zones. In the south of 
Scotland, along with the dormant form, we find the same Clima- 
cograptus and a Dimorphograptus, and here also Monograptus is 
absent, but appears in the succeeding zone, (11) In the Mono- 
—— Monograptus gregarius = Zones of | 
