1909.] 



RECENT BIOLOGV OF SOME LIVING SHELLS. 



753 



Here then we have a possible explanation of the problem we 

 are seeking to solve, namely the presence of J/y« arenana at 

 Uddevalla. It would seem that this very littoral shell belongs to 

 the older and lower bed at Uddevalla, which consists of shallow- 

 water and littoral shells, and that it was possibly extermniated m 

 these northern waters by a sudden subsidence of then^ feedmg- 

 ground, which introduced conditions of much greater depth m 

 the sea-bottom, or by some other similar revolution ; and that 

 the bed on which they lie represents a phase of the recent history 

 of the marine fauna of Scandinavia not recorded ni the books 



Text-fig. 236. 



Text-fig. 237. 



Lateral and dorsal views of shell of M,,a arenaria; from Prof. W C. Brogger's 

 ' Om de senglaciale og postglaciale Nivatorandringar i Knstianiafeltet, by kind 

 permission of the author. 



and perhaps older than some would credit. It seems to me, in 

 fact to represent the penultimate stage in the history of the 

 submarine fauna in the Swedish and Norwegian waters, answer- 

 ing^ probably to the later Crag beds of England. It is possible 

 that the bed at Kadland may represent the same horizon. In 

 this way, and in this way only, can I explain the former presence 

 at Uddevalla of a shell like Mi/a arenaria, which after having 

 been extinct in these waters for at least 8000 years has now 

 invaded them again and has rapidly occupied a much wider area. 

 Suppose we accept this view as a tentative one, and proceed a 



