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



Suborder 2. Pleuronectoidea. 



Dorsal fin extending 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. 

 Vertebrae never fewer than 28 (9 + 19). 



Division 1. Pleubonectiforhes. 



Mouth usually terminal, with the lower jaw prominent ; 

 praeoperculum with free margin. Nasal organ of blind side 

 near edge of head. Optic chiasma monomorphic, 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 laminae 

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

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

 present. 



Subfamily 1. Pabalichtsinje. 



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

 situated behind the cleithra, either symmetrical or with the 

 fin of the e} r ed side nearly median in position. Vertebrae 

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

 praecaudal region downwardly directed, united or connected 

 by bridges to form closed haemal arches; caudal vertebrae 

 without transverse apophyses. 



Principal genera : — Tephritis, Verasper, Uippoglossina, 

 Lioglossina, Xystreurys, Paralichthys, Pseudorhombus, Bamu- 

 laria, Ancylopsetta, JVotosema, Gastropsetta, Cyclopsetta, 

 Syacinm, Azevia, Citharus, Citharichthys, Thysanopsetta } 

 Ktropus, 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), Citharichihys (11 + 28), 

 and Syacium (10 + 25). 



