46 



of the clay deposits into two subdivisions: the fauna of the clay plains and 

 that of the clay channels. 



Common to both, however, is among other things, the coinplete want of 

 vegetation, as also the huge niultitudes in which Brissopsis lijrifera occurs. 

 The latter, which is seeu pretty frequently on c. 15 fathoms, increases very 

 much in numbers, as the bottom becomes softer on accouut of the increasing 

 depth. In the deep clay channel it is so common, that it sometimes makes it 

 very difficult to investigate tliese depths. The otter-seine may be filled with 

 the soft clay and with Brissopsis by the barrel, to the destruction of the rest 

 of the contents — or, as it sometimes liappens, the seine luirsts while it is 

 hauled up, on accomit of the huge weight. 



By attaching a coir rope, 2 — 3 inches thick, to the foot-rope of the 

 seines, we can prevent, however, that it cuts deeply down into the soft bot- 

 tom, by which means the destruction by clay and Brissopsis is diminished. 



a. The Clay Plains. (20—30 Fathoms). 

 The Journal-numbers: 94, 00, 85, 89, 27, 54, 76, and partly: 113, 116 & 105—106. 



As the natural condition of the ground in this region in many respects 

 agrees with that of the mixed deposits, so the fauna shows a great similarity to 

 that of the latter, with respect to the species that occur here; on the other hånd, 

 the nnmber of specimens is considerably changed. Several species which were 

 common on the mixed deposits, become rare here, and vice versa. Some forms 

 seem to be quite missing, while a few ones have been added. 



Of the flat-fishes, for instance, the plaice, the brill, and the common 

 dab become rare, and disappear quite before 30 fathoms. 



The halibut and the turbot are, on the whole, so rare in the northern 

 Cattegat that nothing eau be said about them for certain. 



On the other hånd, the lemon dab and, particularly, the long rough 

 dal) occur in greater numbers than on the mixed deposits; and, finally, a new 

 species of flat-fish makes its appearauce on these depths: 



The pole dab {Pleuronecfes cynoglossus), which, however, does not breed 

 in the Cattegat, but on still deeper water (see the chapter on the Skager Rack). 



Of the codfishes we find here nearly the same species and numbers 

 as on the deepest parts of the mixed deposits; but the specimens are oftéh 

 large, particularly the haddocks. 



On the softest parts of the clay plains occurs the four-be ard ed rocklin g 

 (Onos chnbrhts). 



As our plaice-seine fishermen chiefly fish for the plaice, it does not pay 



