PLEURONECTIDiB. 5 



Dr. Sauvage has remarked that the various degrees of development of the 

 termination of the vertebral column in the genera lihombus, Solea, and Fleuronectes 

 are in accordance with their geological appearance (Compt. Rend., April, 1872), 

 "while, geologically speaking, they are a modern family of fishes, having been 

 found in a fossil state in the early Tertiary deposits (Rhombus solea), but no 

 remains of allied forms occur associated with those of the bony fishes of the 

 Cretaceous and Jurassic rocks. 



Geographical distribution. — These littoral forms are mostly found where the sea 

 possesses a sandy bottom, or else in muddy or sandy rivers, rarely existing at 

 great depths, and but seldom frequenting rocky or precipitous coasts ; while due 

 to the deficiency of an air-bladder they live at the bottom. Pleuronectoids are 

 most numerous towards the tropics, where, however, they do not attain to so large 

 a size as those which reside in temperate or cold regions ; they are absent from 

 very high latitudes. Some, as the common flounder, are anadromous forms, but 

 the majority are strictly marine ; while a few of the marine species have 

 naturally, or consequent upon experiments made by man, been acclimatized in 

 fresh water. 



Synopsis of Genera. 

 A. Jaws and dentition about equally developed on both sides. 



1. Sippoglossus. — Eyes on the right side. Teeth in the upper jaw in two rows. 

 The dorsal fin commences above the upper eye. Scales cycloid. 



2. Hippoglossoides. — Eyes on the right side. Teeth small and in a single row. 

 The dorsal fin commences above the upper eye. Scales ctenoid. 



3. Rhombus. — Eyes on the left side. Teeth in a band in both jaws and present 

 on the vom^er. 



4. Zeugopterus. — Eyes on the left side. Teeth in a band. The dorsal fin 

 commences before the eyes. Scales ctenoid or spinate. 



5. Arnoglossiis. — Eyes on the left side. Teeth in one or two rows in the 

 jaws. Dorsal fin commences on the snout. Scales deciduous. 



B. Jaws and dentition most developed on the blind side. 



6. Fleuronectes. — Eyes on the right side. Teeth of moderate size. The dorsal 

 fin commences above the upper eye. Both pectorals present. 



7. Solea. — Eyes on the right side. Teeth small, only on the blind side. The 

 dorsal fin commences before the upper eye and is not confluent with the caudal. 

 Pectorals may be well developed, rudimentary, or absent. Scales ctenoid. 



Genus I — HiPPOGLOSSTJS, Guvier. 



Platysomatichthys, Bleeker (lateral-line having a curved anterior portion). 



Branchiostegals seven : pseudobranchim present. Eyes on the right side. Gleft 

 of mouth deep. Gill-rahers few, compressed and short. Teeth in the upper jaw in 

 two rows, the outer of which is composed of conical ones : those in the lower jaw conical 

 and widely set : none on vomer, palatines or tongue. Dorsal fin commences above 

 the orbit : caudal free :■ dorsal and anal fin rays {except the last few) unbranched. 

 Scales small, cycloid and not extended on to the vertical fins. Lateral-line straight 

 or with a curve in its anterior portion. 



Habitat. — North Atlantic to the south coast of England, and stragglers o£E 

 France : and on the American coast from Newfoundland to Cape Hatteras. In 

 the North Pacific it has been taken from Kamtskatka to California. 



These fishes are mostly captured ofi" banks at some distance from the coast, and 

 at depths up to 150 fathoms. They attain to a large size. Storer records an 

 American example which weighed 3 cwt. 



1. Hippoglossus vulgaris, Plate XOIV. 



Sippoglossus, Rondel, xi, c. 16, p. 325 ; Willughby, p. 99, t. F6 ; Ray, Syn. 

 p. 33 ; Gesner, pp. 669, 787 ; Aldrov. ii, c. 43, p. 238. Passerimi genus majus, 



