FISHES PLEURONECTIDAE. 



145 



composed of highly bifurcated ray s. The anal fins are continuous in the same manner as the 

 second and third dorsals. Indeed nothing is more alike in shape and structure than those 

 opposite fins. The first anal has the general shape, the same length as the second dorsal, its 

 depth alone heing somewhat less than the height of the latter ; and the second anal is the 

 counter part of the third dorsal. The origin of the anterior anal fin is situated opposite the 

 third ray of the second dorsal, whilst the posterior rays of the second anal and the third dorsal are 

 perfectly even. The second anal fin is higher than the first, which completes the resemblance 

 alluded to. The vent is situated close to the anterior margin of the anal fin. The insertion of 

 the ventrals is placed under a line intersecting the middle of the opercle ; these fins are 

 composed of seven bifurcated rays. The pectorals are long and slender ; their base is situated 

 in advance of the anterior margin of the first dorsal, their extremity extending posteriorly to 

 a vertical line which would be drawn immediately in advance of the origin of the anterior anal 

 fin. The formula of the rays is as follow : 



Br. VII : VII ; D 10, 20, 22 ; A 20, 22 ; C 7, 1, 11, 10, 1, 6 ; V 7 ; P 14. 



The scales are of moderate development, sub-elliptical in shape, and cycloid in structure, 

 with traces of radiating furrows upon their anterior section only. Minute scales are observed 

 on the upper surface of the head, opercular apparatus, and temporal region ; the cheeks, 

 properly so called, are scaleless. The lateral line is very conspicuous ; starting from the upper 

 part of the thoracic belt it undergoes a slight depression under the anterior half of the second 

 dorsal fin, keeping nearer the back than the belly, thence extending straightway to the base of 

 the caudal fin along the middle of the flanks. 



The ground color is uniformly greyish brown above, and silvery grey beneath. The upper 

 surface of the head is quite dark, whilst the cheeks are of a pure silvery hue. The fins being 

 unicolor as far as we could ascertain. 



References to the figures. Plate XLa, fig. 1, represents Homalopomus trowlridgii, somewhat 

 reduced in size. Fig. 2 is a scale from the dorsal region. Fig. 3, a scale from the lateral line. 

 Fig. 4, a scale from the abdominal region. 



List of specimens. 



Family PLEURONECTIDAE, Bonap. 



We meet here with a curious anomaly in the general law of symmetry, for, in the fishes which 

 compose the present family, one of the sides acquires a marked preponderance over the other 

 side, owing chiefly to the position of the eyes on the side just alluded to ; it may be on the right 

 or on the left. The rule is pretty constant amongst the species, and if we do occasionally 

 observe individuals of the same species with the eyes on either side, one is the rule, the 

 other the exception ; for, in many instances, the rule holds good for entire genera where 

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