On the Development of the Pleuronectidai. 219 



Donovan is said to have mistaken one of these abnormally 

 developed specimens for a new species, and to have called 

 it Pleuronectes cy clops. 



In the summer of 1863, I myself obtained, in dredging 

 over a sandy bottom in the Firth of Forth, three young 

 Pleuronectida?, each about half an inch long, and ap- 

 parently belonging to the genus Platessa. In all but one, 

 the eyes and dorsal fin were conformed exactly as in an 

 adult flounder, but the remaining one, which I have the 

 pleasure of exhibiting to the Society to-night, has one eye 

 on the middle line of the top of the head, with, as in M. 

 Van Bencden's specimen, the dorsal fin stopping short 

 behind it. 



As regards the imperfectly developed or monstrous flat 

 fishes already referred to, I am enabled to exhibit to you to- 

 night a specimen of a turbot presenting the peculiar con- 

 dition of the eyes and cephalic extremity of the dorsal fin 

 characteristic of those specimens. Through the kindness of 

 Professor Goodsir, I have also had an opportunity of dissect- 

 ing a similarly malformed flounder {Platessa jiesus). 



These malformations are flat fishes in which the turning 

 round of the upper eye to the other side of the head has 

 been arrested when it has got about the middle line of the 

 top of the head ; and in consequence the passage forwards, 

 and tying down of the anterior part of the dorsal fin, has also 

 been stopped, or obviously it would cross over the eye in- 

 stead of passing by the side of it, as it ought to do. It 

 accordingly projects upwards and forwards in a free pointed 

 process, overhanging the eyes, as may be seen in the speci- 

 men on the table. It is worthy of remark that all these ab- 

 normal specimens are equally coloured on both sides, as if the 

 animal, not having perfectly acquired the characteristics of a 

 flat fish, swam with either of its sides upwards at pleasure, or 

 it might be that it swam, not on its side, but with its mesial 

 plane vertical, as in an ordinary fish. In the specimen on 

 the table, it will also be observed that not only are both sides 

 coloured, but that the rough bony tubercles, usually charac- 

 teristic only of the ocular side of the turbot, arc here also 

 equally abundantly distributed on the opposite one. 



VOL. III. - v 



