28 P. A. øyen [No. 12 



described in my paper: 'Transitional Quaternary Strata of 

 Bentse, Christiania' (Christiania Vid.-Selsk. Forh. 1913, Nr. 6). 



Then a highly interesting series is met with, viz. that of 

 Portlandia lenticula. This species is a wide-spread one in 

 our postglacial clay deposits. In our present sections it appears 

 in the Horten-division of the Søreng period at Braarudaas, and 

 we may trace this species through the sections of Søreng, and 

 Holsbækken, and in the three rather complicate sections of 

 Rakkestad, Spydeberg, and Berger. This species is found as 

 well in the peripheric facies of the Portlandia-slage as more 

 specially in many places as a deep-water mollusca of the Litto- 

 rma-stage. To this fact I directed attention on some former 

 occasions, for instance in a paper on 'Lærumskredet' (Nyt Mag. 

 for Naturv. Vol. XLVII (1909), pp. 239, 240) and in my above 

 mentioned paper on 'Transitional Quaternary Strata of Bentse, 

 Christiania' (Christiania Vid.-Selsk. Forh. 1913, Nr. 6, pp. 8—10). 

 As representing the deep-water deposits of the later part of the 

 Littorina-stage, however, we meet with another rather prominent 

 species, viz. Area pectunculoides. This geological relation be- 

 tween Portlandia lenticula and Area pectunculoides is indicated 

 also through the present distribution of these species (G. 0. Sårs 

 Mollusca Regionis Arcticae Norvegiae, 1878, pp. 39, 43). Area 

 pectunculoides we may trace through the sections of Søreng, and 

 Spydeberg. 



Before entering upon the bearings of such species as Pecten 

 septemradiatus, Macoma baltica and Mytilus edulis we are 

 to scrutinize the stratigraphical position of the last mentioned 

 species more in detail. In a former paper, 'The Quaternary Section 

 of Kilebu' (Christiania Vid.-Selsk. Skr. I. Mathm.-Naturvid. Kl. 

 1912, Nr. 8) I have tried to give some correlative views founded 

 upon the investigation of a well developed shell-bank of southern 

 Norway. And, in the above lines part of the lower portion of 

 it was correlated with the lower part of the Rakkestad section 

 as it was found most probable that the layers C, D and E of 

 this section had to be correlated with almost the whole of part 



