FAMILY, III— PLEURONECTID^. ^.21 



B. Anacanthini, Pleuronectoidei. 

 Structure of head apparently unsymmetrical on the two sides. 



Family, III— PLEURONECTIDiE, Flemming. 



Heterosomata, Bonaparte. 



Pseudobranchiffi 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 tne 

 very young) placed on the superior or coloured surface, sometimes rudimentary. The two sides ot tbe neaci 

 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 hn. 

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

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

 "amoncrst the coral reefs where the Plem-onectida; are frequently found, their tails are often ornamented with 

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

 are half buried, are as duU and dingy as the sm-face 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 Plenronedes, are m 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. mi- • i 



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

 unequal row in the jaws : lateral-line straight. m i,i i? • • 



3. Pseudorhomhits. Eyes on right side. Dorsal fin commences before the eyes. Teeth o± upper jaw in 

 two rows. Lateral-line with a strong curve anteriorly. . in 



4. Platophrys. Eyes on left side. Dorsal fin commences before the eyes. Teeth m a smgle or double 

 row. Lateral-Hne with a strong curve anteriorly. 



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



5. Solea. Eyes on right side : pectorals, if present, usually rudmientary : vertical fins not confluent. 



Scales ctenoid. . , ^ , a i. a i 



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



and anal rays scaled. Scales cycloid or ctenoid. -cr i- i c a + 



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

 Scales ctenoid or cycloid. i . i v 



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

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



Genus, 1 — Psettodes, Bennett. 



Sphagomorus, Cope. 



Branchiostegals seven. Cleft of mouth deep, the maxilla being about half the length of the head. Gill. 

 membranes scarcely united at the throat : gill-rakers replaced by groups of minute spines. Eyes on the right or left 

 side. Jaws and dentition nearly equally developed on both sides. Tivo rows of curved, slender, sometimes barbed, 



* Hr Malm (Srensk. Vet. Akatl. Hnndl. vii, No. 4, 186S) has shown that the skull is only apparently asymmetrical. The 

 youDK Pleuronectoid is obliged, owing to the depth of its body, increased by the development of the vertical hiis, to lie on one side when 

 resting on the ground, as the horizontal fins are not sufficiently developed to sustain it m a vertical position, ihe eye ot 

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



frame-work of the skull. . , , ^ ^, -i- <• ,i, i i ■ i 



t The terms right {deximl) or left (sinistral) are employed in these fishes with respect to the position ot the coloured side. 

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



