266 fF, A. BATHER [ocroBER 
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 Oscidians “have a distinctly Arctic stamp.” 
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 molluses of Arctic Norway, those of the Sound are 
smaller no more often than they are the larger, or of equal size. The 
molluses of the Mediterranean are usually larger than those of the 
Sound, but the contrary is sometimes the case. The molluses 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 16 species of the higher Crustacea, 7 are northern; 4 
wide-ranging and reaching the Arctic; 3 arewest 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; 12 are wide-ranging, but at least two-thirds of these have 
