COMPARATIVE STUDY OF SCOMBROID FISHES. 
309 
small in Acantliocybium (fig. 31), Gramrnatorcynus (fig. 62), and Sarda (fig. 
32). In the Thunnidæ these fins are falcate, conspicuously developed, and 
interspinous bones supporting fin-rays of these fins are remarkably broad. 
In some forms of Neothunnus mcicropterus these fins are unusually de¬ 
veloped, brightly coloured, and their tips nearly touch the terminal points 
of the caudal. In tunnies as well as in Cybium these fins gradually elongate 
with the age of the fish. In immature tunnies and also in bonitos the 
second dorsal and anal are smaller than the first dosral (figs. 43, 53-56). 
These fins are very small in the Katsuwonidæ, especially in the- degenerated 
genera, Euthynnus and Auxis. 
The caudal fin is strong and lunate. Its two lobes are nearly equal in 
size and form, but the upper lobe is often slightly larger. In the Scombridæ 
the fin-rays are soft, thin, and transversely articulated. Iu the Cybiidæ the 
size of the caudal is comparatively large, and its fin-rays are thick, and 
non-articulated. The longest fin-ray in one lobe of the fin makes an angle 
of ca 60° with the longest in the other lobe. The fin-rays next on each side 
of the median fin-ray project posteriorly at the middle (figs. 31, 36). In the 
Thunnidæ the fin-rays of the caudal are so thick and robust, that prehistoric 
fishermen apparently used it for spear-lieads. A specimen of such an im¬ 
plement 21 cm. long, carved from one of these fin-rays of our common tunny, 
was discovered by Mr. Genshichi Yendo in a shell-mound in Miyatojima 
near Sendai, Miyagi-ken. The angle made by the longest fin-rays in the two 
lobes of the caudal is more than 90° in the Thunnidæ and Katsuwonidæ. 
Fin-rays of the caudal of the striped bonito are sometimes used as tooth-picks 
after being cleaned and bleached. Among the so-called scombroid fishes in 
our waters the caudal fin is largest in Cybium chineuse, the length of its upper 
lobe being longer than the height of the body, and ca. 1/4 the length of the 
body (fig. 34). In Cybium guttatum (fig. 61) the caudal fin is also very large. 
SKELETON. 
The Scombridæ, Cybiidæ, and Plecostei differ a great deal from each 
other in the skeleton, the fundamental structure of the body. There seems to 
be very little relation between the skeleton of the Scombridæ and that of the 
Cybiidæ ; but the gradual transformation of the skeleton of the Cybiidæ to 
