Perhaps allied to the Plagyodontidæ is also the large family of Enchodontidæ, widely represented in the Cretaceous rocks of Syria, Europe, and Kansas. The body in this group is elongate, the teeth very strong, and the dorsal fin short. Enchodus lewesiensis is found in Mount Lebanon, Halec sternbergi in the German Cretaceous, and many species of Enchodus in Kansas; Cimolichthys dirus in North Dakota.
Remotely allied to these groups is the extinct family of Dercetidæ from the Cretaceous of Germany and Syria. These are elongate fishes, the scales small or wanting, but with two or more series of bony scutes along the flanks. In Dercetis scutatus the scutes are large and the dorsal fin is very long. Other genera are Leptotrachelus and Pelargorhynchus. Dr. Boulenger places the Dercetidæ in the order Heteromi. This is an expression of the fact that their relations are still unknown. Probably related to the Dercetidæ is the American family of Stratodontidæ with its two genera, Stradodus and Empo from the Cretaceous (Niobrara) deposits of Kansas. Empo nepaholica is one of the best-known species.
Fig. 98.—Eurypholis freyeri Heckel. Family Enchodontidæ. Cretaceous. (After Heckel; the restoration of the jaws incorrect.)
Fig. 99.—Argyropelecus olfersi Cuvier. Gulf Stream.
The Sternoptychidæ.—The Sternoptychidæ differ materially from all these forms in the short, compressed, deep body and distorted form. The teeth are small, the body bright silvery, with luminous spots. The species live in the deep seas, rising in dark or stormy weather. Sternoptyx diaphana is found in almost all seas, and species of Argyropelecus are almost as widely distributed. After the earthquakes in 1896, which engulfed the fishing villages of Rikuzen, in northern Japan, numerous specimens of this species were found dead, floating on the water, by the steamer Albatross.
The Idiacanthidæ are small deep-sea fishes, eel-shaped and without pectorals, related to the Iniomi.
Order Lyopomi.—Other deep-sea fishes constitute the order or suborder Lyopomi (λυός, loose; πῶμα, opercle). These are elongate fishes having no mesocoracoid, and the preopercle rudimentary and connected only with the lower jaw, the large subopercle usurping its place. The group, which is perhaps to be regarded as a degenerate type of Isospondyli, contains the single family of Halosauridæ, with several species, black in color, soft in substance, with small teeth and long tapering tail, found in all seas. The principal genera are Halosaurus and Aldrovandia (Halosauropsis). Aldrovandia macrochira is the commonest species on our Atlantic coast.
