PHYSICAL AND BIOLOGICAL CONDITIONS IX THE NORTH SEA. 251 



How far the movements of these fundicolous species are influenced 

 by the seasons we have very little evidence to show. 



I think that it will be found that the occasional immigrants are 

 usually taken in the area in summer, i.e., during the period when the 

 water is warm. I obtained a specimen of Mustelus vulgaris off 

 Lowestoft on September 18th, The grey gurnard is not such a 

 distinctly southern form as the latchet, nor is the red, Trigla cuculus. 

 On board the steam-trawler Lucania, to the south of the Horn Eeef in 

 May, no latchets were taken, while northern forms, such as haddock, 

 were abundant, and one halibut was taken. Grey gurnard were 

 plentiful. Latchets were plentiful off Amrum in June, and on the 

 Brown Eidges in September. 



It will be found that the abundance of these forms in the Heligoland 

 Bight is in proportion to the degree of their restriction to a southern 

 habitat. The turbot, brill, and sole are fairly common along the north- 

 east coast of England, while turbot and brill extend along the east 

 coast of Scotland, accompanied by Trigla cuculus. As for the weevers, 

 I do not think they are rightly said by Heincke to be common in the 

 neighbourhood of Heligoland, as I did not meet with them there, nor 

 at Grimsby, and although Mcintosh records them as not uncommon 

 at St. Andrew's, this may mean merely that a few specimens are seen 

 every year. They were certainly abundant on the Brown Eidges in 

 September. 



It is well known that in hard winters soles are caught by the 

 trawlers principally in the deeper depressions in the North Sea, 

 especially in the Great Silver Pit south of the Dogger Bank. The 

 latter is an isolated depression, and being cut off from the influence 

 of the water in the deep valley along the north-east coast of Britain, 

 probably contains warmer water than that valley in winter. The 

 physical condition of such depressions in winter does not appear to 

 have been examined, but the fact that soles collect in the Great Silver 

 Pit in winter indicates that the species we are considering are affected 

 by the fall in the temperature of the shallow eastern and southern 

 waters in the coldest months of the year. At present I have no 

 further knowledge of the relative abundance of the southern fun- 

 dicolous species in the southern area and the Heligoland Bight from 

 December to April. 



The third class of southern species in the same region comprises the 

 littoral species, which live principally among the sea-weeds of the 

 littoral zones, and belong chiefly to the families of wrasses, pipe-fishes, 

 gobies, etc. The commonest of these at Heligoland are : Gdbius minutus, 

 the Sand Goby ; Ncrophis aequoreus, the Snake Pipe-fish ; Ctcnolahrus 

 rupesti'is, the Goldsinny. Less abundant are : Sgngnathus acus, the 



