56 



B. SYSTEMATIC PART. 



Order HETEROSOMATA. 



Allied tu the I'crcoinorphi, but asymmetrical, with both eyes on one side of the 

 head. Body strongly compressed, with the pra;caudal region short ; tlorsal and 

 anal fins long ; caudal fin generally with 17 principal rays (15 branched) or fewer ; 

 pelvic fins generally with 6 rays or fewer, thoracic or jugular, with the pelvic bones 

 directly attached to the cleithra. Air-bladder absent in the adult. Mouth more or 

 less protractile, bordered above by the prsmaxillaries only. Parietals separated by 

 the supra-occipital ; interorbital bar mainly formed by the frontal of ocular side ; 

 frontal of blind side extending to prefrontal external to upper eye ; no orbitosphenoid. 

 Pectoral arch attached to skull by a forked post-temporal ; no mesocoracoid. N'erte- 

 bral column of solid centra coossified with the arches ; posterior pra;caudal vertebra? 

 with downwardly directed parapophyses. 



Five families 



SVNOPSIb OF THE FAMILIES. 



I Dorsal fin not extending forward on the head, the anterior rays spinous ; 

 each pelvic fin with a spine and 5 soft-rays : maxillary with supple- 

 mental bone ; palatines tootlied ; vertebr;e 24 (lo ■ 14) ; eyes on the 

 right or left side i. PsETTODiDAi. 



II Dorsal fin extending forward on the head at least to above the eye, none 

 of the rays spinous ; pelvic fins without spines ; maxillary without 

 supplemental tmne ; no palatine teeth ; vertebr;e never fewer than 



28 (9 + 19). 



A. I'raeoperculum with a free margin ; lower jaw generally prominent ; 



nasal organ of bhnd side generally 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 ; one or two post- 

 cleithra on each side : ribs present. 

 I. Eyes on the left side (except in reversed examples) ; nerve of the 

 right eye always dorsal ; egg with a single oil-globule in the yolk 



2 BoTHin.i.. 

 z. Eyes on the right side (except in reversed examples) : nerve of the 



left eye always dorsal ; egg without oil-globules . 3. I'LKiiROXKCTiD.ii. 



B. rra?opercular margin not free, hidden by the skin and scales of the 



head ; lower jaw never prominent ; nasal organs symmetrical 

 in position ; optic chiasma dimorphic, the right or the left nerve 

 dorsal without reference to dextrality or sinistrality : no post- 

 cleithrum ; no ribs, 



1. Eves on the right side ....... 4. Soleid.t;. 



2. Eyes on the left side 5. Cvnoglossid.i-. 



