Zoe BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
LowER MIDDLE ORDOVICIAN. 
As has already been stated, there is throughout northern Europe, 
a distinct change in fauna after the deposition of the last of the strata 
correlated above with the Beekmantown of America. 
In Russia, in Vastergétland, and on Oeland, where there is a con- 
tinuous section of calcareous strata this change is less marked than in 
Norway, where the Gigas limestone is succeeded by black shales, but 
it is shown as well in Scania where the strata of the section are mostly 
shales. 
In Russia, C; marks the introduction of the Echinosphaerites- 
Christiania fauna, in which nearly all the species are different from 
those found in the strata below. In Norway, the Gigas limestone is 
followed by black shales with the Didymograptus geminus fauna, and 
in Scania the shale with Phyllograptus cf. typus is followed by shale 
with Didymograptus geminus. On Oeland, the Gigas limestone is 
followed by limestone with Asaphus platyurus, and that in turn by 
limestone with Illaenus chiron and Didymograptus geminus. 'Through- 
out Scandinavia then, the zone with Didymograptus geminus is the 
earliest zone of the series succeeding the Arenig. In Great Britain 
likewise there is a zone of Didymograptus murchisoni, a species practi- 
cally identical with D. geminus, which is considered as the lowest zone 
of the Llandeilo. In Great Britain there are two species of Dicello- 
graptus in the fauna of this zone, and no species of either Phyllo- 
graptus or Tetragraptus are present. The latter statement is true 
also of Scandinavia, and the zone is known at all localities as being 
the oldest in which there is a profusion of diplograptids. This zone 
is not yet positively identified in America. Ruedemann has provi- 
sionally correlated the Bed 7 of the Deep Kill section of New York 
with the European strata containing the Didymograptus murchisoni 
fauna, but although Phyllograptus and Tetragraptus were not found 
by Ruedemann, the remainder of the fauna is so nearly identical with 
the fauna of the Diplograptus dentatus zone of the Lévis section, where 
both Tetragraptus and Phyllograptus do occur, that I am inclined to 
believe that the zone 7 belongs with the Lévis. 
In Scandinavia the Didymograptus geminus beds are followed by the 
Lower Dicellograptus shales, containing the zones, in ascending order, 
of Glossograptus hincksi, Climacograptus putillus, and Nemagraptus 
gracilis. Unfortunately, a great deal remains to be done before a very 
satisfactory correlation of the Echinosphaerites limestone of Norway 
