364 Proceedings of the Royal Physical Society. 



grouping, based on those characters which appear common to 

 each group, those of generic value being omitted : 



f A. Jaws and dentition about equally developed on both sides ; cleft of 

 mouth, deep. 



(1.) Eyes on right side, j H^ppogloss^is 

 "• ^ -} " ' ( Hippoglossotdes. 



H ( Rhomhus. 



w / (2.) Eyes on left side, < Zeugopterus. 



§ \ ( Arnoglossus. 



p^ 



w I B. Jaws and dentition more developed on the blind side ; eyes on the 

 ^ I right side ; cleft of mouth, shallow. 



Pleuronectes. 

 Solea. 



The three genera with the eyes on the left side include, in 

 the main, the species comprised in Klein's genus Rhomhus, 

 as originally constituted. All possess the following, amongst 

 other characters, not including characters common to the 

 PleuTonectidm generally : Branchiostegals, usually seven ; eyes 

 on the left side ; teeth in a band, usually villiform, none on 

 the palatines ; dorsal fin commences considerably in front of 

 the eyes ; most of its rays, and those of the anal, branched 

 (except in A. later na). 



The continuation of the dorsal fin on to the snout, and the 

 situation of the eyes on the left side, are points which in 

 themselves are sufficient to distinguish Rhomhus and its allies 

 from all other British Pleuronectidm. 



The following characters appear to be of constant occur- 

 rence in the genus Zeugopterus, and therefore serve to dis- 

 tinguish its species from Rhomhus on the one hand, and 

 Arnoglossus on the other. 



Genus Zeugopterus, Day (Gottsche). 



Rhomhus (in part), Klein. 

 Lepidoi^homhus (in part), Gottsche, 

 Zeiigopterus, Gottsche. 

 Phrynorhombics, Giinther. 



Dorsal and anal fins continued under the caudal, forming 

 a small flap ; ventral fins united with the anal, or overlapping 

 its anterior extremity ; scales, ctenoid and ciliated, usually 

 with one or more spinous processes on the free margin. 



