684 



TELEOSTEI 



CHAP. 



Fam. 2. Amphistiidae. — The only known representative of 

 this family, the Upper Eocene Anij^histium 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. — 'Ri&iors.tioTi. ot Amphistium 2Mradoxum. x\. 



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. 



