90 ANNALS OF SCOTTISH NATURAL HISTORY 



been completed, while the anterior extremity of the dorsal 

 fin projects forward in the form of a pointed process. In 

 such cases the fish is usually equally pigmented on both sides. 

 It might be considered to be a matter of indifference as 

 to which of the eyes should leave its own side and pass over 

 to the other, but, as a matter of fact, different groups of 

 flat-fishes are characterised by a pretty constant position of 

 the eyes on one side or on the other. For example, in the 

 Halibuts, the Flounders, and the Soles, the normal position 

 of the eyes is on the right side, while in the Turbots and in 

 the Plagusiae they are found on the left. 



Exceptions to the general rule of the group to which a 

 flat-fish may belong are not unc .nmon. The appended cut 

 shows a sketch of the head of a specimen of the Common 

 Flounder (Pleuronectes flesus, Linn.) from the river Esk at 



Musselburgh, in which the eyes, instead of being on the 

 right side, as is normal for the genus, are on the left, as in a 

 Turbot. In every other respect, except the transposition of 

 the blind and ocular sides, the specimen is normal. 



EXPLANATION OF PLATE I. 



Fig. I. Profile view of head of malformed Trout from Dunipace, showing the 

 abnormally short lower jaw. Natural size. 



Fig. \a. The same head seen from below. 



Fig. 2. Profile view of the head of another specimen, showing the lower jaw, 

 of more than the usual length. Slightly reduced. 



Fig. za. The same head seen from below, showing the want of symmetry in 

 the right and left rami of the mandible. 



