146 U. S. P. R. R EXP. AND SURVEYS ZOOLOGY GENERAL EEPORT. 



the eyes are placed either on the right or on the left side. The side on which the eyes are 

 situated is generally the one where the diversity of coloration is displayed, whilst the other is, 

 generally speaking, colorless, else unicolor. This circumstance is easily accounted for by the 

 oblique position these fishes assume in their native element ; the colorless side being directed 

 downwards, is placed in almost the same position as the abdominal region in the other member 

 of the class. 



The body of these fishes is very flat and very much compressed, sub-elliptical in general 

 outline, short or elongated, according to the genera. The dorsal fin extends the whole length 

 of the back, the anal occupying mostly the entire region from the vent to the caudal fin. The 

 pectorals, when extant, are equally developed; they are wanting in some species. The ventrals 

 being inserted under the thoracic belt. 



The position of the eyes on one side being the result of a torsion of the bones of the cranium, 

 the mouth is variously distorted, and varies also very much in size. The maxillar teeth are 

 more developed on the side where the eyes are situated, being sometimes entirely absent from 

 the other side. The palate is toothless. The scales are of the ctenoid type to a few exceptions 

 which are cycloid in structure. There is no air bladder. 



SYN. Pleuronectidae, BONAP. Sagg. distr. anim. vetebr. 1831, 117. 

 Platessoideae, RICHARDS. Faun. Bor. Amer. Ill, 1836, 255. 

 Planidae, D E KAT, New Y. Fauna, IV, 1842, 293. STOKER, Synops. 1846, 223. 



According to the observations made by Yan Beneden, the young of this family at the period 

 of hatching present a symmetrical form equal to that of any other fish, the assymetry being 

 brought about during their ulterior growth. It has also been observed that while yet immature, 

 and when the eyes have already assumed their final situation, the young flat fish swims in a 

 perfectly horizontal position, the dorsal and abdominal outlines being on the same level, 

 whilst they take and keep an oblique position so soon as their growth is completed. 



There are two species of this family mentioned by Dr. Ayres as occurring on the Pacific 

 coast of North America, specimens of which we have not seen. One is a &quot; Halibut,&quot; supposed 

 to be identical with Hippoglossus vulgaris (Proc. Cal. Acad. Nat. Sc. 1855, 41), seldom found 

 so far south as the entrance of the Bay of San Francisco, though very abundant further north, 

 whence it is brought to the San Francisco market. 



The other is a &quot; Flounder,&quot; and has been described under the name of 



Platessa UUncata, AYUES, in Proc. Cal. Acad. Nat. Sc. 1855, 40. 



It is taken in the Bay of San Francisco and brought to the market of that city. 



PARALICHTHYS, Girard. 



GEN. CHAR. Eyes moderate, situated on the right side. Mouth largo ; snout sub-conical ; jaws sub-equal. Slender and 



conical teeth on both sides of the jaws. Origin of dorsal fin situated in advance of the orbits. Dorsal and anal fins not 



continuous with the caudal ; latter sub-truncated posteriorly. Surface of the head scaly as well as the body. Lateral line 

 arched above the pectoral fins, hence straight to the base of the caudal. 



The general aspect of the body is elongated and ellipsoid, reminding us of certain species of 

 the genus Platessa, whilst the gape of the mouth resembles more that of Rhombus. 



