1899] THE FAUNA OF THE SOUND 265 
and of the nature of the bottom, in which latter the varying character 
of the flora must be included. 
Here we cannot reprint the annotated faunal list given by Dr. 
Lonnberg ; nor is this needed, since the universal language of systematic 
zoology will enable any one specially interested to learn from the 
papers themselves what species have been found. 
The list of fish is complete, being supplemented from other sources 
than Dr. Lonnberg’s own captures. It includes 98 species, of which 
92 are purely marine. Of these latter, 41 are southern forms, 
stretching down to the Mediterranean, and never passing above the 
Arctic circle; 30 are northern forms, stretching from the Arctic seas 
no farther south than the English Channel; 11 have an intermediate 
or West-European distribution ; while 10 have a wider and less deter- 
mined range. But when we consider the distribution of those fish 
that are permanent inhabitants of the Sound, or that appear there 
regularly year after year, the proportions are reversed. Such species 
number 47, and of them 14 are southern, 22 northern, 6 intermediate, 
and 5 wide-ranging. Comparison with neighbouring areas brings out 
several points of interest, of which a few may here be noted. The 
fish - fauna of Helgoland is less numerous (78 species), but as a 
whole the proportions of northern, southern, and intermediate forms 
are about the same as for Oresund. Among permanent inhabitants, 
however, Helgoland reckons a larger percentage of southern forms. 
The west Baltic has a fish-fauna of about 95 species. Many of these 
are fresh-water forms, of which only a few occur in the Sound. Of 
the salt-water forms almost all occur in the Sound, which also contains 
21 species not found in the west Baltic. These latter, however, are 
more or less occasional visitors, and of them 10 are southern, 3 northern, 
6 intermediate, and 2 wide-ranging. 
In this fish-fauna the oldest stock consists of the northern species, 
which could live in these regions during or soon after the glacial 
period. Then, too, their range extended farther to the south, so that 
most of them reached the coast of France, and some got even as far as 
Spain. For others, however, such as Dyrepanopsetta platessoides, the 
southern limit was already reached in the Sound. A final class con- 
sists of pure relict forms, such as Lumpenus lampetriformis and 
Cyclogaster liparis. As the climate improved, species of southern 
origin could by degrees settle in the Sound. 
The occasional visitors in the fish-fauna follow the various kinds 
of water in the marine currents; thus the southern species come with 
the warmer and salter water in summer and autumn. When the con- 
ditions are altered by an influx of some other water, also when the 
temperature is lowered, many of these fish sicken and are thrown up 
on the beach, so that just before winter many southern fishes are found 
in this way. The southern immigrants are observed from June to 
December. The northern species that come with currents from the 
