230 BULLETIX: MUSEOI OF COMPARATIVE ZOOLOGY. 



graptoides zone succeeds the Ceratopyge zone, and precedes the Lim- 

 bata Umestone. The Planilimbata Hmestone can not be older than 

 the oldest of the Tetragraptus zones. On Oeland, Isograptus gibber- 

 nlus, and other graptolites of the Lower Didyniograptus zone occur 

 in the Lower Asaphus limestone, which Lamansky correlates with the 

 Russian zone ^m^. In Norway the Gigas limestone is followed by 

 black shale with Didymograptus geminus. On Oeland, the Gigas 

 limestone is followed by the Platyurus limestone, and that in turn by 

 the Chiron limestone, which contains Didymographis geminus. The 

 top of the Gigas limestone, and like^s'ise of the Orthoceras limestone 

 (Bjxi-y) of Russia, is therefore somewhat older than the Didymographis 

 geminus fauna. In Scania, the Didymograptus geminus fauna is found 

 in shales resting on other shales containing Fhyllograptus cf. typus and 

 Didymograptus cf. hifidus. This in turn rests upon the Orthoceras 

 limestone of that region. This limestone, in turn follows shale with 

 the Isograptus gibberulus fauna. The limestone contains a large 

 trilobite fauna which, however, in our incomplete knowledge of the 

 faunas of the Swedish "Orthoceras limestone," it is not safe to corre- 

 late directly with the faunas of other regions. Since it follows the 

 zone with Isograptus gibbcridus, one would natm-ally correlate the 

 Orthoceras limestone of Scania with the Lower Asaphus limestone of 

 Oeland. If this correlation is correct, then the PhyUograptus cf. 

 typus beds of Scania would appear to represent some or all the Upper 

 Asaphus limestone, Gigas limestone, and Platyurus limestone of 

 Oeland. But for reasons to be given later, the Plat^nirus limestone is 

 probably to be eliminated from this list. This does not of course, 

 prove definitely that the Gigas limestone is of the age of PhyUograptus 

 cf. typus, though there is a strong presumption, since both are older 

 than the zone with Didymograptus geminus. Fortunately however, 

 Schmidt found PhyUograptus in Bm in Esthonia, and PhyUograptus 

 sp. has been reported from above the Gigas limestone of Norway. 



The limestone of the Gigas and lower zones, down to the bottom of 

 the Plamlimbata zone of Sweden, and the zones Bn and Bm of Russia 

 must therefore be placed within the range of PhyUograptus in the 

 graptolite succession. It remains now to see what that means in the 

 American sequence. 



The occurrence of the Tetragraptus-Phyllograptus-Didymograptus 

 fauna in the shales of the Levis formation of Canada has long been 

 known, and recent work by Ruedemann (115) and the writer (111) 

 has shown the order of succession of the faunules within the forma- 

 tion. The relation of the Levis to the Beekmantown of America 



