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 ; 3 are northern forms, stretching from the Arctic seas 

 no farther south than the English Channel ; 1 1 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 1 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 Drepanopsetta platcssoides, the 

 southern limit was already reached in the Sound. A final class con- 

 sists of pure relict forms, such as Lumpciuis lampctriformis and 

 Cjjdogaster 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 



