=Suborder Zeoidea.=—Not far from the _Selenichthyes_ and the _Berycoidei_ we may place the singular group of John Dories, or zeoid fishes. These have the ventral fins thoracic and many-rayed, the dorsal fin provided with spines, and the post-temporal, as in the _Chætodontidæ_, fused with the skull. Dr. Boulenger calls attention to the close relation of these fishes to the flounders, and suggests the possible derivation of both from a synthetic type, the _Amphistiidæ_, found in the European Eocene. The _Amphistiidæ_, _Zeidæ_, and flounders are united by him to form the group or suborder _Zeorhombi_, characterized by the thoracic ventrals, which have the rays not I, 5 in number, by the progressive degeneration of the fin-spines and the progressive twisting of the cranium, bringing the two eyes to the same side of the head. It is not certain that the flounders are really derived from Zeus-like fishes, but no other guess as to their origin has more elements of probability. [Illustration: FIG. 195.—_Semiophorus velifer_ Volta. Eocene. (After Agassiz, per Zittel.) ] We may, however, regard the _Zeoidea_ on the one hand and the _Heterosomata_ on the other as distinct suborders. This is certain, that the flounders are descended from spiny-rayed forms and that they have no affinities with the codfishes. [Illustration: FIG. 196.—_Amphistium paradoxum_ Agassiz. Upper Eocene. (Supposed ancestor of the flounders). (After Boulenger.) ] =Amphistiidæ.=—The _Amphistiidæ_, now extinct, are deep-bodied, compressed fishes, with long, continuous dorsal and anal fins in which a few of the anterior rays are simple, slender spines scarcely differentiated from the soft rays. The form of body and the structure of the fins are essentially as in the flounders, from which they differ chiefly by the symmetry of the head, the eyes being normally placed. _Amphistium paradoxum_ is described by Agassiz from the upper Eocene. It occurs in Italy and France. In its dorsal and anal fins there are about twenty-two rays, the first three or four undivided. The teeth are minute or absent and there is a high supraoccipital crest.