Isospondyli 273 
of the milkfish. The commonest species is Hiodon tergisus. 
No fossil Hiodontide are known. 
The Pterothrisside.—The Piterothrisside are sea-fishes like 
Albula, but more slender and with a long dorsal fin. They live 
Fic. 206.—Istieus grandis Agassiz. Family Pterothrisside. (After Zittel.) 
in deep or cold waters along the coasts of Japan, where they are 
known as gisu. The single species is Pilerothrissus gissu. The 
fossil genus Istzeus, from the Upper Cretaceous, probably be- 
longs near the Pterothrisside. Istieus grandis is the best-known 
Fig. 207.—Chirothriz libanicus Pictet & Humbert. Cretaceous of Mt. Lebanon. 
(After Woodward.) 
species. Another ancient family, now represented by a single 
species, is that of the Chirocentride, of which the living type 
is Clirocentrus dorab, a long, slender, much compressed herring- 
like fish, with a saw-edge on the belly, found in the East Indies, 
