OF THE BRITISH ISLANDS. 79 



British species it is the right-hand side which lies upper- 

 most, and is consequently coloured, the reverse, however, ob- 

 taining in the Turbot {Rhombus maximus), No. 126 ; the Brill 

 {Rhombus Icevis), No. 127 ; Eckstrom's and Midler's Top- 

 knot {Zeugopterus unimaculatus) and Z '. punctatus),^ os. 128 

 and 129 ; and the Sail-fluke and Megrim {Arnoglossus megas- 

 toma and A. latenia), Nos. 130 and 131. Reversed examples 

 of a normally right or left coloured species are, however, not 

 unfrequent, as also so-called " double " examples, in which 

 the characteristic colour is developed on both sides of the 

 body, and " albinos," with both surfaces more or less com- 

 pletely colouress. Examples illustrating all of these abnormal 

 developments will be found in the spirit-preserved series in 

 the Day Collection. The largest British representative of the 

 Pleuronectidse is the Halibut, or Holibut {Hippoglossus 

 vulgaris), No. 124, taken in the North Sea, but attaining 

 to its largest dimensions in the colder waters off Newfound- 

 land, Greenland, and Iceland. An example is recorded by 

 Olassin to have been captured near the last-named station, 

 that measured but little short of twenty feet, while a length 

 of six or seven feet, with a weight of from 300 to 500 lbs. 

 is of frequent occurrence. The long rough Dab {Hippogloss- 

 oides limandoides), No. 125, much resembles the Holibut in 

 its proportions, but rarely exceeds a length of twelve or 

 fifteen inches, and is distinguished from it among other points, 

 according to Dr. Day's ' British Fishes,' by the possession 

 of a strong, spur-like spine developed in front of the anal 

 fin, which, according to the same authority, is absent in the 

 Holibut. In the type specimen of the last-named fish con- 

 tributed by Dr. Day to the Buckland Museum, there is, 

 nevertheless, an exceedingly strong spine developed in the 

 position indicated, while in that of the Rough Dab it is 

 scarcely perceptible. In several other Flat fish, including 



