ÖFVERSIGT AF K. VETENSK.-AKAD. FÖRHANDLINGAR 1 8 94, N:0 10. 583 



a frontal ridge divided into tive tubercles as in the plaice; the 

 shapes of the head, eyes and mouth are also the same as in 

 the plaice as well as the number of rays of dorsal and anal 

 fins. But it differs from the plaice in the smallness ofitshead, 

 the less depth of its body, the shorter distance between its anal 

 hn and the tip of its snout, in its pectoral fin being smaller 

 and its scales larger. The last characteristic obviously reminds 

 US of some other species of flounders and therefore I will make 

 a short comparison between them and this form. If Ave then 

 begin with the dab (Pleuronectes limanda) we shall tind that 

 some characteristics of the specimen we are considering resemble 

 those of the dab, for instance the relative length of head 

 and depth of body, but other measurements are very different. 

 The most important characteristic, however, is the form of the 

 lateral line. In the dab it is strongly curved, in the plaice less 

 so, ^) but yet it is curved. In this variety, on the contrary, it 

 is almost perfectly straight. Of course its anterior part is 

 turned a little upwards, it does not however become arcuated. 

 Thus this aberrant specimen can not be a cross between two 

 forms with curved lateral lines. As the dab and the plaice do 

 not spawn at the same time, the hybridisation between them is 

 still more unlikely, not to say impossibie. The dab spawns in 

 the vicinity of Anholt in the Cattegat in May and the first 

 part of June;^) thus at the time of my visit in the middle of 

 June most specimens of this kind were very meagre and thin, 

 since their spawning season was över; the plaice on the con- 

 trary, were at that time about as fat as possible. 



If the form in question is a cross between the plaice and 

 some other Scandinavian flounderfish, one would expect the latter 

 to have larger scales and a straighter lateral line than the 

 plaice. These two conditions are to be found fulfilled in the 

 case of Drepanopsetta platessoides and Pleuronectes cynoglossus. 



^) The plaice is rather variable in this respect. 



^) On the 12th of June I obtained one specimen with roe; all the others 

 very väst number — were already empty. 



