256 PHYSICAL AND BIOLOGICAL CONDITIONS IN THE NOKTH SEA. 



Gulf Stream is diminished, and an influx of cold water 4° to 5" C. takes 

 place into the Baltic, from the north along the Norwegian coast. 



Five of these occasional immigrants are absent from the Heligoland 

 region, namely, Liparis Montagui, Stichaeus idandicus, Brosmius hrosme, 

 Pleuroncdcs cynoglossiis, and Raia radiata. These are also wanting in 

 the southern shallower part of the North Sea, that is to say, south of 

 the 20 fathom line, except Liparis Montagui, which, according to Day, 

 occurs at the mouth of the Thames and on the south coast of England. 

 These five are the most especially northern of the above list, and are 

 true Arctic species. Liparis Montagui is common along the east coast 

 of Scotland and north-east coast of England. Of Stichaeus islandicus, 

 only one or two specimens have been taken occasionally in the north- 

 western part of the North Sea, once in 40 fathoms off St. Abb's Head, 

 once in February, 1894, ofl' the mouth of the Firth of Forth, and two 

 specimens in July, 1892, 240 miles E. h N. from Spurn Head. 

 Brosmius hrosme, the tusk or torsk, is abundant from Spitzbergen to the 

 Shetlands, but further south becomes scarcer: it has only been 

 occasionally taken off the Yorkshire coast. Pleuronectes cynoglossiis, 

 the witch, is abundant on the Great Fisher Bank, and may be said to 

 be limited in the North Sea by the 30 fathom line. Baia radiata has 

 a similar distribution, not being found south of Yorkshire. 



Two species found in the Heligoland region have not been taken 

 in the Baltic, namely, Carelophus ascanii, of the blenny family, and the 

 rockling, Motella mustcla. The former is common on the north-western 

 coast of Norway, and occurs rarely on the east coast of Britain as far 

 south as Yorkshire. Motella mustcla extends southwards throughout 

 the southern area of the North Sea, and occurs also on the south coast 

 of England. 



The other three occasional immigrants into the Western Baltic, 

 namely, the cat-fish, the coal-fish, and the halibut, occur along the east 

 coast of Britain as far to the south as the 30 fathom line, but not south 

 of it. 



Hippoglossoides limandoides, the long rough dab, is resident in the 

 Baltic, and also in the north part of the North Sea, north of the 

 30 fathom line, but is absent from the Heligoland region, and from the 

 shallow southern area. 



The other species mentioned in the above list, although not entirely 

 absent from the southern area and the eastern slope of the North Sea, 

 become much scarcer there, as will be seen from the observations in 

 these areas recorded in the two previous numbers of this Journal. The 

 lemon dab (Pleuronectes microcepkaUis) is found more plentifully along 

 the English coast in the southern area, i.e., along the line of deeper 

 water. Lepidorhomhus megastoma, the megrim, is a northern form, not 



