492 Mr. C. T. Ecgan on the Origin and 



Suborder 2. Pleuronectoidea. 



Dorsal fin extendinoj forward on the head at least to above 

 the eye; all the fin-rays articulated; each pelvic fin of 6 or 

 fewer rays. No supramaxillary bone; no palatine teeth ; 

 lower edge of urohyal deeply emarginate, so that the bone 

 appears forked. On each side a single post-cleithrum or none. 

 Yertebrge never fewer than 28 (9 + 19). 



Division 1. Pleu ronectifo smes. 



Mouth usually terminal, with the lower jaw prominent ; 

 pr8eo})erculum with free margin. Nasal organ of blind side 

 near edge of head. Optic chiasma nionomorphic, the nerve 

 of the left eye in dextral forms and that of the right eye in 

 sinistral forms always dorsal. A post-cleithrum; ribs present. 



Family 1. Bothidae. 



Sinistral, except for reversed examples in certain species. 

 Nerve of the right eye always dorsal. Olfactory laminai 

 arranged transversely to, or radiating from, a central rachis. 

 Egg with a single oil-globule in the yolk. Pectoral radials 

 present. 



Subfamily 1. Paralicstsinje. 



Pelvic fins short-based, supported by the pelvic bones and 

 situated behind the cleithra, eitlier symmetrical or with the 

 fin of the eyed side nearly median in position. Vertebrae 

 33-41 (9-12 + 24-30) ; most or all of the parapophyses in the 

 prajcaudal region downwardly directed, united or connected 

 by bridges to form closed hajmal arches; caudal vertebrae 

 without transverse apophyses. 



Principal genera : — Tephritis^ Verasper, Ilipjyoglossina, 

 Lioglossina, Xystreurys, Paralicht/iys, PseudorhoinbuSj Uamu- 

 laria, A/icylopsetta, JSotosema, Gastropsetta, Cyclopsettaf 

 Syacium, Azevia, Citharus, Citha^nchthys, T/iysunopsetta, 

 Etropus, from tropical and temperate seas. 



In most the mouth is moderately large, with the jaws and 

 dentition nearly equally developed on both sides; but in the 

 small-mouthed Etropus the jaws of the blind side are curved 

 and are much more strongly toothed than those of the eyed 

 side. 



I have examined the skeletons of Paralichthys (vertebrae 

 10 + 24), Pseudorhombus (10 + 27), Citharichthys (11 + 28), 

 and Syacium (10 + 25). 



