458 Sir H. H. Eoivorth—The Western Baltic. 



Echinus drohachiensis. Ophiura textiirata. 



Echinocymmis angidosus. Nonionina crassula. 



Amphidetus cordatus. Bulimina scabra. 



OphiophoUs aculeata. Miliolina seminulum. 



In addition to the eloquent testimony of these lists it should be 

 remembered that in the Sound certainly, and probably in the Belts, 

 the number of species is larger in their northern than their southern 

 parts. The evidence is, in fact, complete and conclusive that these 

 three conduits are mere outlets of the Cattegat, and their contents, 

 like the contents of marine origin in the Baltic, are colonists from 

 that wide arm of the sea, which migrated at the time of the shattering 

 of the ancient land-bridge, and thus became highways by which the 

 salt water of the Cattegat and a portion of its living contents found 

 their way into the Baltic. 



We cannot any longer doubt that the whole of the marine fauna 

 and flora of the Sound, the Belts, and the Baltic are comparatively 

 quite recent immigrants, and that before the breakdown in the bridge 

 just referred to there were none of them to be found south of the 

 northern entrances of the three waterways in question. A parallel 

 case to this breakdown and its consequences is quoted by Eeclus, 

 who says : — 



" The literal ' cordon ' which bounds the Limfiord on the west 

 has been broken down several times by tempests, notably in 1624, 

 1720, 1760, and on Nov. 28th, 1825, when terrible inundations over- 

 whelmed the low districts of the North Sea The outer 



beach of the Limfiord, known as the Harboore Tange, was broken 

 down, and the waters of the lake were once more united to the sea 

 by one of the numerous Nymunde (new mouths). 



" Before the opening of the breach at Agger all the western part 

 of the Limfiord formed a fi-esh-water lake, but the intrusion of the 

 Bea water and the recommencement of a marine current caused great 

 changes. Multitudes of fish entered it, while the proportion of 

 salinity rose to 18 per thousand, and oyster beds were formed here 

 and there. This new entrance was not used for navigation till 

 1854, and it was subject to great oscillation, at one time not having 

 more than 1^ metres on the bar and sometimes 3 metres. In 1863 

 a new mouth was opened at Eon. In 1875 that at Agger was again 

 closed by the sea." ("Nouvelle Geographic," v, 10.) 



What it is a little startling to find, however, is that not only have 

 all the marine forms of life in the Baltic and its three inlets migrated 

 thither recently, but actually in the human period and during tbe 

 so-called Neolithic or second Stone age ; and that all the variations, 

 distortions, and stunting of various forms of marine life in the Baltic 

 which diiferentiate them from the similar forms in the open sea, and 

 which, in this view, become more than ever important and deserving 

 of study, have arisen since man occupied the country. 



It seems to me that this fact makes it very important that all the 

 forms of life in the Baltic should be subjected to a newer and closer 

 analysis than they have yet received, with the object of ascertaining, 

 how far and in what way the marine fauna of the North Sea has 



