COMPABATTVE STUDY OF SCOMBKOID FISHES. 
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forward, instead of turning more or less backward as in the other plecostean 
fishes. Each artery reaching to the myotome of the first rib is divided into 
two arteries, epaxial and hypaxial. The epaxial artery runs below the first 
rib, while the hypaxial artery runs above the rib. These two arteries, are 
nearly equally developed, and are separated from each other at a distance 
of 6-8 times the breadth of the blood-vessels. These arteries do not form a 
loop at the caudal region. The cutaneous artery and cutaneous vein lie 
in juxtaposition, nearly flat at the surface of the body. Arterioles and venules 
connected with these cutaneous canals run in opposite directions, along the 
surface of the body, and they are not so numerous as in the tunnies. The 
rod of the vascular plexus in the haemal canal is called kurochiai by fishermen, 
and it is thicker than the diameter of the vertebral column. 
This genus is closely allied to the genus Neotliunnus of the Thunnidae 
and stands quite near the genus Euthynnus. Number of the precaudal vertebrae 
corresponds to that of Euthynnus, while the number of caudal vertebrae is 
equal to that of the Thunnidae. Thus the total number of vertebrae is 41, 
while in all the other genera of the plecostean fishes the number is always 39. 
Only one cosmopolitan species is known from the temperate and tropical 
regions of the world. 
Katsuwonus pelamis (Linnaeus). 
Katsuwo, magatsuwo, mandaragatsuwo. 
Figs. 5, 14, 19, 25, 52, 57. 
Scomber pelamis, Linnaeus, Syst. Nat. X, 297, 1758. 
Thynnus pelamys, Cuv. & Val., Hist. Nat. Poiss. VIII, 113, Tab. 214, 1831 ; Schlegel, Fauna 
Japon. Poiss, 96, Tab. 49, 1850; Günther, Cat. Brit. Mus. II, 334, 1860. 
Gymnosarda pelamis. Dressier & Fesler, Bull. U. S. Fish Comm. VII, 436, 18S9, Jordan 
& Evermann, Fish. N. & M. America, I, 868, 1896. 
Euthynnus pelamis, Tanaka, Fish. Japan, I—X, 140, Pis. 37, 39, 40, 1912. 
Katsuwonus pelamys, Kishinouye, Sui. Gak. Ho, I, 21, PI. 1, Fig. 14, 1915. 
D. 12-17, 11-14, 8. A. 11-15, 7. Gill-rakers 15-20+36-39. 
Body plump, sharply pointed at both ends. Lateral line slightly curved 
upward above the pectorals and bent below the second dorsal, and nearly 
horizontal in the caudal portion. Gill-rakers numerous, very thin, and their 
inner margin undulating. The right lobe of the liver is small and slender. 
Plexus of venules from the posterior cardinal vein forms a long continuous 
