The Tension of Carbonic Acid affecting tbe Structure 

 and Preservation of Molluscan Shells. 



Investigations in the Baltic. 



I have made some determinations of the carbonic acid- 

 tension in the Baltic in order to test a suggestion made by 

 Mr. Ad. Jensen of the Copenhagen Zoological Museum. Mr, Jensen 

 had observed that some species of Bivalves from certain High- 

 Arctic localities, notably along the east-coast of Greenland, 

 presented very marked peculiarities with regard to the structure 

 and thickness of the shells. I shall enumerate some of the 

 most striking examples leaving it to himself to treat the matter 

 adequately from a malacological point of view. 



The periostrakum of Astarte borealis is in these localities 

 extremely thick and bast-like. In the Danish seas Dr. Joh. 

 Petersen found that this was likewise the case in the Baltic, 

 while the same species, living in the Kattegat, has a normal, 

 thin periostrakum. Mr. Jensen thinks it probable that this 

 thickness of the periostrakum may act as a protection against 

 dissolution. 



Tellina calcaria, whose shells are normally rather solid, 

 is found in the same High-Arctic localities and also in the 

 Baltic, around Bornholm, with extremely thin and fragile shells, 

 often bearing strong indications of their having been exposed 

 to chemical attack from the water. 



Dead shells, which everywhere else greatly outnumber the 



25' 



