250 niYSICAL AND BIOLOGICAL CONDITIONS IN THE NORTH SEA. 



continental rivers, than to a greater flow of salt water from the Straits 

 of Dover. At any rate, so far as I understand it, the physical evidence 

 does not show that there is an inflow of Channel or Atlantic water 

 corresponding to the immigration of southern aperticolous fish, while 

 the higher temperature which does correspond to that immigration 

 appears to be caused by the warming of the land and shallow water by 

 the summer sun. 



On the other hand, the Pomerania observations actually prove that 

 in the deeper north-western depression the bottom water was frequently 

 below 8° C, and that the passage of this cold water southwards was 

 arrested by the Dogger Bank. I think it would be more correct to say 

 that the boundary of this cold water to the south and east is the 

 25 fathom line. It is reasonable to infer that although the temperature 

 at the actual surface in summer on the north-east coast of England is 

 by no means low enough to account for the absence of mackerel, 

 anchovy, etc., yet the influence of the cold water below is sufficient to 

 restrict these southern species to the region south and east of the 

 25 fathom line. 



We proceed next to the consideration of the southern species of 

 fundicolous or bottom fishes in the Heligoland Bight and southern area 

 of the North Sea. The list of these is rather a long one. The 

 commonest of them are : Ehomhus maximus, the Turbot ; Ehomhns lacvis, 

 the Brill ; Solca vulgaris, the Sole ; Solca hitea, the Solenette ; Trigla 

 gurnardus, the Grey Gurnard ; Trachinus draco, the Greater Weever ; 

 Trachinus vipcra, the Lesser Weever. 



Less abundant are : Trigla hirnndo, the Tub or Latchet ; Trigla cuculus, 

 the lied Gurnard ; Mullus harhatus, the Red Mullet ; Callionymus lyra, 

 the Dragonet ; Arnoglossus laterna, the Scaldfish ; Galeus vulgaris, the 

 Tope. 



Heincke does not mention Trachinus vipcra among the fishes of 

 Heligoland. In the voyage of the John Bull off Amrum in June, I 

 saw nothing of either species of weever, but both were very common on 

 the Brown Eidges off the Dutch coast in September. 



Heincke believes Tryjla cuculus to be absent, but I saw specimens, 

 identified with certainty, taken frequently in the trawl in my voyages 

 both north of Heligoland and on the r>rown llidges. 



As occasional immigrants the following species occur : Lahrax lu2ms, 

 the Bass ; Zeus faher, the John Dory : Gadus luscus, the Pout or Bib ; 

 Motclla tricirrata, the Three-Bearded Rockling ; Conger vulgaris, the 

 Conger ; Mustclus vidgaris, the Smooth Hound ; Scyllium canicula, the 

 Small Spotted Dog-fish; Trygon pastinaca, the Sting Ray. 



To the fundicolous forms may be added Amphioxus lanceolatus, which 

 burrows in the sea-bottom, and is common near the Horn Reef. 



