366 FISHES 



A very remarkable structural peculiarity occurs usually in 

 specimens which are completely ambicolorate, or nearly so. 

 This has been observed most frequently in the turbot and 

 flounder, especially in the former, but is not unknown in other 

 species. It consists in the condition of the anterior end of the 

 dorsal fin, the attachment of which stops short behind the upper 

 eye, while the fin itself projects forwards as a hook-shaped pro- 

 cess as seen in Plate XXX., Figs. A and B; the upper eye 

 itself also seems to lie on the edge of the head and to be 

 directed more outwards than in normal specimens. A speci- 

 men of the turbot in this condition was formerly described 

 as a distinct species under the name Pleuronectes cyclops, and 

 the malformation is sometimes described as cyclopean, but 

 there is no union of the two eyes to justify the use of this 

 term. In the turbot and flounder, as well as in the brill and 

 plaice, this malformation of the head is always present in com- 

 pletely ambicolorate specimens, and in the turbot when only 

 the head region of the lower side is white the malformation 

 also occurs, but when the coloration of the lower side is of 

 less extent the malformation is wanting and the head is normal. 

 On the other hand, ambicolorate specimens of the sole and lemon 

 sole {Pleuronectes microcephalus) have been observed in which 

 no malformation of the head occurred. 



Cases of the opposite kind of abnormal coloration in which 

 more or less of the upper side is white like the lower are not 

 uncommon in the plaice and in other species, and usually the 

 white area of the upper side is sharply separated from the 

 adjacent coloured surface. I have seen a sole twelve inches 

 long in which the whole of the upper side was white like the 

 lower, except the head and part of the tail-fin. 



The most remarkable abnormality known in flat-fishes is 

 that of a small turbot not quite two inches long which was cap- 

 tured in 1906 on the coast of Cornwall ; in this fish (Plate 

 XXX., A, B) the right side was white as usual, and the left 

 side was normally coloured except on the head ; but both eyes 

 were on the right uncoloured side instead of the left ; the mal- 

 formation of the head above described was also present, the 

 anterior end of the dorsal fin projecting forwards in a free, 

 hook-shaped process. This specimen when alive rested on the 

 ground with its white side and the eyes directed upwards, and 



