Evolution of the Order Heterosomata. 493 



Subfamily 2. Platorkrinm. 



Pelvic fin of blind side short-based ; pelvic fin of ocular 

 side elongate, extending forward to theurohyal, supported by 

 a cartilaginous plate placed in advance of the cleithra. Verte- 

 brae 37-43 (9-10 + 27-33) ; parapophyses in prascaudal 

 region connected or united as in the Paralichthinas ; caudal 

 vertebrae with well-developed transverse apophyses. 



Principal genera : — Arnoglossus, Anticitharus, Chascano- 

 psetta, Pelecanichthys, Scceops, Engyprosopon, Lceops, Mono- 

 lene, Trichopsetta, Platoplirys, Lepidopsetta, Lophonectes, 

 from tropical and temperate seas. 



In the small-mouthed Lceops the jaws and dentition are un- 

 equally developed on the two sides, just as in Etropus. 



I have examined skeletons of Arnoglossus (vertebras 10 + 33), 

 Platoplirys (10 + 29), and Lophonectes (10 + 31). 



Subfamily 3. Botsinje. 



Both pelvic -fins elongate, extending forward to the urohyal, 

 supported by cartilaginous plates placed in advance of the 

 cleithra. Vertebras 35-41 (9-12 + 25-31); parapophyses in 

 precaudal region separate ; caudal vertebras with well- 

 developed transverse apophyses. Jaws and dentition equally 

 developed on both sides. 



Genera: — Bothus, Lepidorhombus, Zeugopterus, and Phryno- 

 rhombus, from the North Atlantic and Mediterranean. 



I have examined skeletons of Bothus (vertebras 11 + 25), 

 Lepidorhombus (9 + 31), Zeugopterus (9 + 26), and Phryno- 

 rhombus (10 + 26). 



Family 2. Pleuronectidas. 



Dextral, except for reversed examples in certain species. 



Nerve of the left eye always dorsal. Olfactory laminae 



slightly raised, parallel, without rachis. Egg without oil- 

 globules. 



Subfamily 1. Pleuronectinxi. 



Anterior part of dorsal fin posterior to nasal organ of blind 

 side ; pelvic fins short-based, supported by the pelvic bones 

 posterior to the cleithra, similar in form and symmetrical, or 

 the fin of the eyed side median. Pectoral radials present ; 

 hypocoracoids narrowed forward below. Vertebras 35-65 

 ( 10-16 + 23-52); prascaudal parapophyses separate, divergent. 



