606 
ACTIXOPTERTGII. 
prtxctirsor, 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 : — 
Otolithus ( Macruridarum ) bavaricus, E. Koken, Palaeontogr. 
vol. xxxviii. (1891), p. 37, fig. 1. — Upper Cretaceous; 
Siegsdorf, Bavaria. 
Otolif, Juts ( Macruridarum ) singularis, E. Koken, Zeitschr. deutsch. 
geol. Ges. vol. xliii. (1891), p. 98, pi. vi. fig. 9. — Lower 
Oligocene ; Lattorf. 
Family PLEURONECTIDiE. 
Trunk deepened, much laterally compressed and flattened, the 
fishes always resting on one side when adult. Skull unsym- 
metrically developed, and both eyes in the adult situated on the 
one sido which is always coloured and turned upwards when at rest. 
Premaxilla excluding maxilla from gape. Abdominal region very 
short. Paired fins small, often un symmetrically developed, and one 
or more sometimes absent. Dorsal and anal fins much extended, 
not subdivided. In the recent forms : — gills four ; pseudobranchue 
well developed ; air-bladdor 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 It. H. Traquair, Trans. Linn. Soc. vol. xxv. (I860), 
pp. 263-296, pis. xxix.-xxxii. 
Genus RHOMBUS (Klein), Cuvier. 
[Regnc Animal, vol. ii. 1817, p. 222.] 
Mouth wide, the jaws and dentition being nearly equallj 
developed on both sides ; a narrow band of villiform teeth, without 
canines, on the margin of the jaws ; equally small teoth also on the 
vomer hut not on the palatines. Eyes on the left sido. Gill-rakers 
woll-developed, lanceolate ; seven branchiostegal rays. Abdomina 
vertebra; with broad transverse processes, and very small delicate 
ribs ; hasmal spines at base of caudal fin somewhat expanded, not 
fused together. Both pairs of fins present, usually unsymmetrically 
developed ; dorsal tin arising on the snout ; caudal flu separate, 
rounded behind. Scales small or absent. 
