684 



TELEOSTEI 



Fam. 2. Amphistiidae. The only known representative of 

 this family, the Upper Eocene Amphistium paradoxum, originally 

 described as a Pleuronectes, has much in common with the Zeidae, 

 from which it differs in the smaller number of vertebrae (10 + 

 14), and in the dorsal and anal spines being more reduced, adnate 

 and continuous with the series of soft rays ; the scales are more 

 normal and imbricate ; ventral fins with 1 spine and 8 soft rays. 

 This fish appears to realise in every respect the prototype of the 

 Pleuronectidae before they had assumed the asymmetry which 

 characterises them as a group. 



FIG. 417. Eestoration of Amphistium paradoxum. x J-. 



Fam. 3. Pleuronectidae. Head asymmetrical, the skull 

 twisted in front, with the two orbits on one side in the adult ; 

 the side of the body bearing the eyes and turned upwards in life 

 being coloured, the other side colourless and blind. Mouth more 

 or less protractile. Gills 4, a slit behind the fourth ; pseudo- 

 branchiae present. Lower pharyngeal bones usually separated, 

 rarely imperfectly united. Vertebrae 24 in the most generalised 

 form (Psettodes), varying from 28 to 65 in others, the praecaudals 

 mostly with more or less developed transverse processes, which 

 may be directed downwards and become converted into haemal 

 arches ; ribs- and epipleurals present. Caudal fin, if well 

 developed, supported by a large hypural usually without basal 

 spine or knob. Dorsal and anal fins much elongate, without spines, 

 the former often extending on the head. Paired fins often reduced, 



