266 F. A. BATHER [october 



north, are usually found from February till April. For all these fish 

 the Sound forms, as it were, a large net with deep and wide intake 

 towards the north, narrowing funnel-wise between Helsingborg and 

 Elsinore, but widening again and deepening by Hven Island and 

 Landskrona ; but for a large part of the migrants the passage is com- 

 pletely closed by the sill-like shoal between Malmo and Saltholm. 



Passing to the lower forms of animal life, Dr. Lonnberg mentions 

 only such as he has himself observed, and gives careful notes on their 

 habitats. The northerly nature of the fauna, already exemplified by 

 the fish, is far more marked among these less wandering groups. 



The Osciclians ''have a distinctly Arctic stamj)." 



Among Mollusca, the bivalve fauna is almost entirely northern. 

 Of 32 species, 14 are purely northern, while all the rest have been 

 recorded from Arctic Norway. Of the 22 prosobranch gastropods, 9 

 are northern, 8 wide-ranging but chiefly northern, 2 wide- 

 ranging but chiefly southern, although they are found at Lofoden 

 as well as among glacial fossils ; 3 alone are purely southern 

 forms. Of the 4 shell - bearing opisthobranch gastropods, 1 is 

 purely southern, but the 3 others, though having a southerly dis- 

 tribution, are found in Arctic regions. The 3 nudibranchs are all 

 northern. Three of the chitons are purely northern ; the 2 others 

 wide-ranging, but do not reach farther north than Lofoden. In short, 

 of all the 68 molluscan species, 42 - 66 per cent are purely northern; 

 the same proportion stretches from the Mediterranean to the Arctic 

 seas; 8*82 per cent find their northern limit at Lofoden; only 5 # 88 

 per cent are purely southern. A comparison of the measurements of 

 55 shell-bearing species from Oresund, the Kattegat, Arctic Norway, 

 Kiel Bay, and the Mediterranean, gives the following results. The 

 molluscs of the Sound are, as a rule, smaller than those of the 

 Kattegat ; those that are larger or of equal size are all Arctic forms. 

 Compared with the molluscs of Arctic Norway, those of the Sound are 

 smaller no more often than they are the larger, or of equal size. The 

 molluscs of the Mediterranean are usually larger than those of the 

 Sound, but the contrary is sometimes the case. The molluscs of the 

 Kattegat are generally larger than those of Arctic Norway. Species 

 that are common to the Kattegat and the Mediterranean are twice as 

 often the larger in the Kattegat. This shows that salinity alone is 

 not the effective factor in this case, but that other causes co-operate. 



Among 1 6 species of the higher Crustacea, 7 are northern ; 4 

 w r ide-ranging and reaching the Arctic; 3 are west European; and 2 purely 

 southern. 



Of the 41 or 44 species of Chaetopoda found by Dr. Lonnberg 

 within the Sound as restricted by him, no less than 25 are purely 

 northern ; 1 2 are wide-ranging, but at least two-thirds of these have 



