﻿SUMMARY OF THE CONTENTS. 711 



known, 245 species, of which 34 are arctic, 102 boreal, and 109 

 lusitanic, or in the proportions 



— ^ a: — ^h:-\- ^l 



(see the table, pp. 557 — 563). As already mentioned, a number 

 of arctic, and a^ few lusitanic species, still occurring in the 

 upper tapes-banks, have disappeared, whereas a far greater 

 number of lusitanic species have immigrated. About 20 species 

 of lusitanic mollusca at present unknown in the upper tapes- 

 banks, are known in the lower tapes-banks of the Kristiania 

 region (see p. 564, where these species are enumerated); also a 

 few boreal species in the lower banks have not hitherto been 

 found in the upper. 



Altogether the lusitanic element of the fauna has increased 

 essentially also in the lowest tapes fauna, partly by immigration 

 of new forms, partly by the predominance of a series of great 

 lusitanic forms, which at that time where more common and 

 widespread than before and after that period. 



Pp. ,570—575. Comparison between the Postglacial and the 

 Present Mollusc Fauna of the Kristiania Fjord. 



Pp. 570—575 contain some remarks upon the definition of 

 the terms: arctic, boreal, and lusitanic. 



P, 576. The entire postglacial fauna of shell-bearing mol- 

 lusca from the Kristiania region comprises 40 arctic, 103 boreal 

 and 112 lusitanic species, total, 255 species. The living mollusc 

 fauna of the Kristiania Fjord comprises 268 species, of which 

 210 also belong to the fauna of the postglacial deposits. 



45 of the postglacial species are hitherto not known as 

 living in the Kristiania Fjord, 14 of them being arctic, 9 boreal 

 and 22 lusitanic (pp. 577, 578). 



On the other hand 58 species now living in the fjord, are 

 not known in postglacial deposits of the Kristiania region; 5 of 

 these species are arctic, 32 boreal, and 21 lusitanic (pp. 578, 579). 



