684 TELEOSTEI CHAP. 
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. 
Fic. 417.—Restoration of Amphistium paradoxum. 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, 
