COMPARATIVE STUDY OF SCOMBROID FISHES. 
457 
They are found not only in both jaws, but also on the palatines and some¬ 
times on the vomer too. Teeth on the palatines are in single row. The right 
lobe of the liver much elongated as in the genus Auxis. It is remarkable 
that the chief cutaneous artery runs along the dorsal external side of the chief 
cutaneous vein, quite contrary to the case in all the other forms of the plecostean 
fishes, and the dorsal segmental branches of the chief cutaneous vein pass 
over the accompanying artery, which is a little more or less deeply imbedded 
in the muscle. The degenerated hypaxial cutaneous artery lies ventral, that is 
external and similarly to the accompanying vein. Hypaxial, cutaneous blood¬ 
vessels are bent in a zigzag line. They have no connection with the vascular 
plexus, nourishing the dark red portion of the lateral muscle. The subspinal rod 
of the vascular plexus is also well developed, but the rod is separated from the 
vertebral column hy the development of the epihaemal process, between the 
vertebral column and the haemal canal. Thus the inferior foramen is remarkally 
larger than in the genus Katsmuonus. 
Dark markings in the naked part of the back, and generally some greyish 
spots in the pectoral region above the ventrals. 
Fishes of this genus attain about the same size as the striped bonito. 
They are degenerated forms, derived from the genus Katsuivonus. Voracious 
fishes of temperate and tropical seas, not forming large schools, and often ap¬ 
proaching the coast. Until recently only one species was known, but I have 
found other two species in the Pacific, quite different from the Atlantic 
species. 
Key to the species of the genus Euthynnus. 
Vomerine teeth present. 
Dark oblique bands on the back. E. yaito. 
Dark longitudinal bands on the back. E. limatus. 
Vomerine teeth absent. E. alleterata. 
Euthynnus yaito Kishinouye. 
Yaito, hiragatsuwo, obosogatsuwo, segatsuwo, suma, uramawarigatsuwo, wata- 
nabe, yaitopara, yaitosuma. 
Figs, 26, 54, 58. 
Thymus thunnlna, Schlegel, Fauna Japon. Poiss. 95, Tab. 48. 1850. 
? Thynnus affinis, Cantor, Cat. Malay. Fish. 106, 1850. 
