on the Obliquity of Flounders. 367 



the head by a simple torsion of the head on its axis; and 

 3rdly, that, after the passage of the eye down upon the left side 

 by a further torsion, the dorsal fin would have continued its 

 progress over the head. So far as this observation goes, these 

 are mere assumptions, according to Professor Steenstrup's view 

 extremely improbable; but all the structural peculiarities of 

 Malm's fish are most simply explicable if we suppose the young 

 of a " double " Rhombus to have fallen into his hands. 



This peculiar malformation is by no means uncommon among 

 Flounders. Its main characters are that both sides are coloured 

 and nearly equally developed, that the eye of the blind side is 

 placed in the middle line at the top of the head, while the eye 

 of the eye side is in its normal position, and that the dorsal fin 

 is arrested immediately behind the upper eye, and sometimes 

 somewhat arched over it. 



Donovan gives the first figure of this monstrosity, under the 

 name of Pleuronectes Cyclops : he imagined it to be a permanent 

 species. His specimen seems to have been a monstrous Brill. 

 Schleep, in the 'Isis' for 1829, describes two "double" indi- 

 viduals of Rhombus maanmus, and states that he had met with 

 others. Several " double '^ Flounders are described from the 

 British coast (Yarrell, Couch, &c.). Among the Plaice, the same 

 monstrosity is cited by Malm and Nilsson in P. Flesus, and 

 by Kroyer in P. vulgaris. Even in the Soles the same peculiarity 

 seems to be indicated by Yarrell in his notice oi Solea Trevelyana. 

 The Holibut [Hippoglossus vulgaris) seems to be the only common 

 form in which a double variety is not described. 



It may seem strange that the single individual taken by Malm 

 should have presented this somewhat unusual modification ; we 

 must remember, however, that while the common herd of "right" 

 and "wrong" Flounders move along the bottom, "double" 

 Flounders come to the surface, and within range of a towing-net. 



V. 



Besides the two marked deviations in form from the normal 

 type of each species (" wrong " Flounders and " double" Floun- 

 ders), there are likewise deviations in colour — "albinos" and 

 "ncgros." Albinos, white on both sides, but yet normal in 

 form, are mentioned by many authors : by Kroyer in Platessa 

 vulgaris and in P. Flesus (quoted from Gottsche) ; by Schleep in 

 P. vulgaris : in this latter case no sexual parts could be detected. 

 Houttuyn describes an albino ; and Shaw's Pleuronectes roseusj 

 from the Thames, belongs to the same category. Flounders dark 

 on both sides, without any structural malformation (negros), 

 seem also to occur, but more doubtfully. They are mentioned 



