746 SIE HENRY H. HOWORTH ON THE [NoV. 9, 



the shell had in fact invaded the Baltic since the kitchen-midden 

 men lived along the fiords of Denmark. Petersen's view is now 

 generally accepted. It is possible, however, and important, to 

 define more definitely the period when the shell first invaded the 

 Baltic. It is first referred to by its recognised name in the tenth 

 edition of the ' Systema Naturse' of Linnaius, in which, however, 

 he mentions that, in his work on his travels in West Sweden, he 

 had already described it under the name Concha arenaceo marino. 

 On turning to this reference, which has not been sufficiently 

 appreciated, I find that he describes the shell at some length 

 among the discoveries he made while at Oerost, an island in the 

 district of Bohuslan, in West Gothland (see ' Wastgota Besa,' 

 1747, p. 187). He adds that he had never found it in any part of 

 Sweden, and clearly implies that he had not seen it until he went 

 to Oerost. In his description of the discovery of the shell he tells 

 VTS how, in searching the tide- washed sands at Oerost, he noticed a 

 number of twin holes here and there unaccompanied by the little 

 mounds of sand thrown up by burrowing worms, and, having put 

 the stem of his long tobacco-pipe in some of them, was surprised 

 to find it had struck against something hard. On burrowing 

 with his hands he came upon the mollusc we call Mya arenaria, 

 and that occasion was apparently the first time it had been 

 noticed that molluscs in shells as well as freely moving worms 

 dig holes of this kind. He goes on to say that the shell was 

 fovind always buried under the sand-flooi^s and never thrown 

 upon the beach. This is confirmed by the habitat he gives the 

 shell in his ' Fauna Suecica,' where he says of it : " Habitat in 

 Oceano Bohuslan alluente." As the visit of Linna3us to Oerost was 

 made in 1747, when he was familiar with the zoology of Eastern 

 Sweden, it amounts to a fairly complete proof that the shell was 

 not living in the Baltic in 1747, and that it was only when he 

 explored the coast of the Cattegat that he first found it. 



Lyell, in the memoir already cited, and writing in 1835, goes 

 on to say that it did not then live in the Bothnian Gulf as far as 

 Sodertelji, that he could not find it even at Oalmar, while further 

 south, at Solvitzborg, it was rare and of very small size {op. cit. 

 p. 10). 



Kojenikof, writing in 1892, says that all the specimens he had 

 found were young, by which he perhaps means they were dwarfed. 

 He mentions its present distribution in the Baltic thus — Rligen, 

 Stralsund, Greifswald, Stolpe, the Bay of Dantzig, Calmarsund, 

 Gotland, near Memel, Libawa, Windawa, near Riga, Dago, Oesel, 

 Hapsal, Matzalwick, Reval, near iN'arva, and the Bothnian Gulf 

 as far north as 62'35 N. This proves how widely and rapidly it 

 had spread in the Baltic since its introduction, and how much at 

 home it now is in brackish water. 



Long ago Dr. J. E. Gray had already said of the species that it is 

 often found so high up the rivers that the water in which it lives 

 is brackish only during high tides, adding that it is found more- 

 over with freshwater shells on the coasts of the Baltic, while all 



