244 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
coryphe, Calymene, Conularia, and Echinosphaerites. The zone is 
forty to forty-five meters thick about Christiania. 
The strata of 4b@ consist of thin-bedded dark blue limestone with 
shaly partings and the thickness is about twelve meters. Here one 
finds much the same fauna as in 4ba, but Christiania has disappeared. 
A Platystrophia of large size, like the P. lynz of the Itfer and Jewe was 
collected from this zone. 
4by is another zone of much shale and some thin-bedded limestone, 
with a variable thickness, usually from thirteen to sixteen meters. 
Chasmops extensa is the guide fossil and Brégger has not listed any 
others. I myself found no fossils worth saving at this horizon. 
4bé, the last of the zones of 4b, consists of interbedded dark blue 
limestone and almost black shale, the thickness being about twelve 
to seventeen meters. In this zone are found the last and the largest 
of the Echinosphaerites, and a very Trenton-like fauna, in which I 
was interested to note two common American forms, a Parastrophia 
somewhat like P. hemiplicata, and a Triplecia very like T. nuclea. 
Cyclocrinites spasskit makes its first appearance in Norway at this 
horizon, and Illaenus, Ampyx, Trinucleus, Remopleurides, Cybele, 
Chasmops, etc., are present. Brodgger (94) correlates this zone with 
the Jewe of Russia with which I entirely agree, only adding that the 
presence of Cyclocrinites spasskw suggests also the Kegel. It seems 
quite possible that there is a break in the sedimentary record in the 
Christiania district at this point. 
In the Christiania area the zone 4bé is followed by the zone 4ca, 
the beginning of the Trinucleus seticornis fauna, correlated with the 
Trinucleus shales of Sweden. In the district Mjésen, north of Chris- 
tiania, however, Holtedahl (97) has found a different succession, 
and strata which, in my opinion, are to be intercalated between 
4bé and 4ca, and not to be correlated with 4c as Holtedahl has done. 
As in Christiania, stage 4 in Mjésen is introduced with an Ogygio- 
caris zone, containing Ogygiocaris dilatata, Didymograptus geminus and 
many other species, this zone having a probable thickness of twenty 
to thirty meters. This is followed by a thin zone of calcareous shales, 
three to four meters thick, and it in turn by black shales with limestone 
nodules, the thickness unknown. The fauna consists very largely of 
gastropods and cephalopods, of which many species are listed. The 
fauna is connected with the preceding zones by’the presence of Ogy- 
giocaris dilatata, but no species pass on into the overlying strata. 
We have here probably a very unusual development of the strata of 
the age of the zone of Nemagraptus gracilis. 
