46 Isospondyli 



of the milkfish. The commonest species is Hiodon tergisus. 

 No fossil Hiodontidce are known. 



The Pterothrissidae. The Pterothrissidce are sea-fishes like 

 Albula, but more slender and with a long dorsal fin. They live 



FIG. 34. Istieus grandis Agassiz. Family Pterothrissidce. (After Zittel.) 



in deep or cold waters along the coasts of Japan, where they are 

 known as gisu. The single species is Pterothrissus gissu. The 

 fossil genus Istieus, from the Upper Cretaceous, probably be- 

 longs near the Pterothris sides. Istieus grandis is the best-known 



FIG. 35. Chirothrix libanicus Pictet & Humbert. 



(After Woodward.) 



Cretaceous of Mt. Lebanon. 



species. Another ancient family, now represented by a single 

 species, is that of the Chirocentrida, of which the living type 

 is Chirocentrus dorab, a long, slender, much compressed herring- 

 like fish, with a saw-edge on the belly, found in the East Indies, 



