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 4bj8 consist of thin-bedded dark blue hmestone 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. lynx of the Itfer and Jewe was 

 collected from this zone. 



4b7 is another zone of much shale and some thin-bedded limestone, 

 with a variable thickness, usually from thirteen to sixteen meters. 

 Chasmops extcnsa is the guide fossil and Brogger has not listed any 

 others. I myself found no fossils worth saving at this horizon. 

 \ 4b5, the last of the zones of 4b, consists of interbedded dark blue 

 Hmestone 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. nitclea. 

 Cyclocrinites spasskii makes its first appearance in Norway at this 

 horizon, and Illaenus, Ampyx, Trinucleus, Remopleurides, Cybele, 

 Chasmops, etc., are present. Brogger (94) correlates this zone with 

 the Jewe of Russia with which I entirely agree, only adding that the' 

 presence of Cyclocrinites spasskii suggests also the Kegel. It seems 

 quite possible that there is a break in the sedimentary record in the 

 Christiania district at this jDoint. 



In the Christiania area the zone 4b5 is followed by the zone 4ca, 

 the beginning of the Trinucleus seticornis fauna, correlated with the 

 Trinucleus shales of Sweden. In the district Mjosen, north of Chris- 

 tiania, however, Holtedahl (97) has found a different succession, 

 and strata which, in my opinion, are to be intercalated between 

 4b5 and 4ca, and not to be correlated with 4c as Holtedahl has done. 

 As in Christiania, stage 4 in ISIjosen is introduced with an Ogygio- 

 caris zone, containing Ogygiocaris dilatata, Didymograptus gcminus 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. 



