FAMILY, III— PLEURONECTID^. 421 



B. Anacanthini, Pleuronectoidei. 



Structure of head apparently unsymmetrical on the two sides. 



Family, III— PLEURONEOTID^, Flemming, 



HeterosowMa, Bonaparte. 



Pseudobranchisa well developed. Gills four. Body strongly compressed, flattened, with one of its sides 

 coloured, the other being destitute of colour, or having merely some spots. Both eyes (except in the 

 very young) placed on the superior or coloured surface, sometimes rudimentary. The two sides of the head 

 not equally developed,* one remaining almost rudimentary. The jaws and dentition may be nearly equally 

 developed on both sides, or more so on the blind than the coloured. A single long dorsal and anal fin. 

 Pectorals, if present, may be rudimentary. Scales present or absent. Lateral-line on the coloured side single, 

 double, or triple, curved or straight. Air-vessel absent. 



Geographical distribution. — These fishes are extended to most regions, residing at the bottom of the sea, 

 some ascend rivers. The upper surface is coroured, and as observed by Adams (Voyage of the Samarang), 

 "amongst the coral reefs where the Pleuronectidse are frequently found, their tails are often ornamented with 

 rather vivid colours, and their upper sides marked with somewhat strildng patterns, whereas those that 

 are half buried, are as duU and dingy as the surface is where they are found." 



Dr. Sauvage (Comp. Rend. 1872, April), has observed that the various degrees of development of the 

 termination of the vertebral column in the genera Rhombus, Solea, and Plewronectes, are in accordance with 

 their geological appearance. 



SYNOPSIS OF GENERA. 



A, Jaws and dentition nearly similar on both sides. 



1. Psettodes. Dorsal fin commences on the neck : eye on right or left side. 



2. Githwrichthys. Dorsal fin commences before the eyes, which are on the left side. Teeth in a single 

 unequal row in. the jaws :' lateral-line straight. 



3. Pseudorhomhus. Eyes on right side. Dorsal fin commences before the eyes. Teeth of upper |aw in 

 two rows. Lateral-hue with a strong curve anteriorly. 



4. Platophrys. Byes on left side, Dorsal fin commences before the eyes. Teeth in a single or double 

 row. Lateral-line with a strong curve anteriorly. 



B. Cleft of mouth narrow, and the dentition on the blind side most developed. 

 6. Solea. Byes on right side : pectorals, if present, usually rudimentary : vertical fins not confluent. 

 Scales ctenoid. 



6. Achirus: Eyes on right side : pectorals, if present, rudimentary : vertical fin not confluent : dorsal 

 and anal rays scaled. Scales cycloid or ctenoid. 



7. Synojptwra. Eyes on the right side : pectorals, if present, may be rudimentary. Vertical fins confluent. 

 Scales ctenoid or cycloid. 



8. Plagusia. Eyes on the left side : pectorals absent : vertical fins confluent. Two or three lateral-lines 

 on the left side : lips with tentacles. Scales ctenoid or cycloid. 



9. Gynoglossus. Eyes on the left side : pectorals absent : vertical fins confluent. Two or three lateral- 

 Hnes on the left side. Lips without tentacles. Scales ctenoid or cycloid. 



Genus, 1 — Psettodes, Bennett. 



Sphagomorus, Cope. 



Bromchiostegals seven. Glefl of mouth deep, the maxilla being about half the length of the head. Gill- 

 membrames scarcely umited at the throat : gill-rakers replaced by groups of minute spines. Ilyes on the right or left 

 side. Jems cmd dentition nea/rh/ equally developed on both sides. Two rows of curved, slender, someti/ines barbed, 



* Hr. Malm (Syensk. Vet. Akad. Handl. Tii, No. 4, 1868) has shown that the skull is only apparently asymmelrical. The 

 young Plenronectoid is obliged, owing to the depth of its body, increased by the development of the vertical fins, to lie on one side when 

 resting on the ground, as the horizontal fins are not sufficiently developed to sustain it in a vertical position. The eye of 

 the "blind" side has a tendency to turn towards the light, in doing so it carries with it the surrounding cartilaginous 

 frame-work of the skull. . . 



t The terms right (dexi/ral) or left (^smisbral) are employed in these fishes with respect to the position ot the coloured side. 

 To ascertain this the fish is placed with its tail towards the observer, the dorsal fin upwards, the anal downwards. 



