606 
ACTII^OPTEEYGII. 
■prcecursor^ E. Koken, Joe. cit. 1891, p. 96, fig. 6; Pliocene, 
Orciano, near Pisa, Tuscany. Purchased, 1875. 
Other supposed otoliths of this family, not represented in the 
Collection, are described as follows :— 
Otolitlius {Macruridarmn') havaricus, E. Koken, Palseontogr. 
vol. xxxviii. (1891), p. 37, fig. 1.—Upper Cretaceous; 
Siegsdorf, Bavaria. 
Otolithus i^Macruridarum) singularis, E. Koken, Zeitschr. deutsch. 
geol. Ges. vol. xliii. (1891), p. 98, pi. vi. fig. 9.—Lower 
Oligocene ; Lattorf. 
Family PLEURONECTIDA:.A.'’»?"f'r'/“^ ' 
A K TCIC . 6 S • 
Trunk deepened, much laterally compres’sed and fiattened, the 
fishes always resting on one side when adult. Skull unsym- 
metrically developed, and both eyes in the adult situated on the 
one side which is always coloured and turned upwards when at rest. 
Premaxilla excluding maxilla from gape. Abdominal region very 
short. Paired fins small, often unsymmetrically developed, and one 
or more sometimes absent. Dorsal and anal fins much extended, 
not subdivided. In the recent forms :—gills four ; pseudobranchise 
well developed ; air-bladder absent. 
This family dates back to the Upper Eocene, but no extinct 
genera are recognisable. In existing seas its range is cosmopolitan, 
and a few forms live in freshwater. 
A description of the skull of some existing Pleuronectids is 
published by K. H. Traquair, Trans. Linn. Soc. vol. xxv. (1866), 
pp. 263-296, pis. xxix.-xxxii. 
^ ^Genus RHOMBUS (Klein), Cuvier. 
' [Eegne Animal, vol. ii. 1817, p. 222.] 
Mouth wide, the jaws and dentition being nearly equally 
developed on both sides ; a narrow band of villiform teeth, without 
canines, on the margin of the juws ; equally small teeth also on the 
vomer but not on the palatines. Eyes on the left side. Gill-rakers 
well-developed, lanceolate ; seven branchiostegal rays. Abdominal 
vertebrae with broad transverse processes, and very small delicate 
ribs; haemal spines at base of caudal fin somewhat expanded, not 
fused together. Both pairs of fins present, usually unsymmetrically 
developed; dorsal fin arising on the snout; caudal fin separate, 
rounded behind. Scales small or absent. 
