in two characters : (1) it is somewhat lighter in colour after death, and instead of large 

 black blotches on the coloured side it has small black specks scattered almost 

 uniformly over the surface ; (2) the anterior nostril of the lower side is very large and 

 conspicuous, it is dilated and has folds radiating from its wall into its cavity. At 

 Plymouth and other places on the south coast of Devon and Cornwall another flat- 

 fish is commonly sold which is called the thick-back. This is evidently a kind, of sole, 

 but is distinguished by its smaller size, and by its colour and marking, which consists 

 of black transverse stripes on a red ground. 



Several kinds of flat-fishes are obtained from British seas, which are too small and 

 too scarce to be of any value as food, but which of course have been studied by 

 zoologists equally with the edible species. 



After studying all the species of flat-fishes brought together in the British Museum 

 from all parts of the world, Dr. Giinther has classified them in thirty-four genera, 

 including Solea. But of these only seven include species which occur on the British 

 coasts. Zoologists often differ as to the limitations of genera, because it is in many 

 cases difficult to decide whether several species differ from one another to an equal 

 degree and ought therefore to be classed in a single genus, or whether they differ in 

 different degrees and ought to be separated into two or more genera. Eecent 

 authorities also recognise seven genera among British forms namely, Hippoglossus, 

 Hippoglossoides, Rhombus, Zeugopterus, Arnoglossus, Pleuronectes, and Solea. The 

 external differences which distinguish the genera and species of British forms may be 

 presented analytically thus : 



A. Eyes on the left side ; mouth terminal ; teeth on both sides ; ventral eye anterior 

 to the dorsal. 



1 . Rhombus. Shape rhomboidal, middle of the body being very broad ; 



mouth large ; lateral line with a semicircular curve anteriorly. 



Rhombus maximus, the Turbot. No ordinary scales, but pointed 

 tubercles uniformly scattered over skin. 



Rhombus Icevis, the Brill. Small scales ; no tubercles. 



2. Zeugopterus. Shape almost rectangular, anterior end obtuse ; lateral line 



with a semicircular curve anteriorly ; scales ctenoid. 



Zeugopterus unimaculatus, first dorsal ray elongated and undivided, 

 median fins not prolonged under the base of the tail ; a conspicuous 

 large dark spot towards the posterior end of the lateral line. 



Zeugopterus punctatus, first dorsal ray not elongated, median fins 

 prolonged under the base of the tail. 



3. Arnoglossus. Shape oval, rather narrow, with sharp snout; eyes large, 



almost level, ventral slightly more advanced. Cleft of mouth deep. 

 Teeth small, one or two rows in both jaws ; present or absent from the 

 vomer ; none on the palatines. Gill-membranes somewhat broadly united 



