COIITAIIATIVE STl'DY OF SCOMBROID FISHES. 309 



small iu Acanfhocybtum (fig. 31), Gi-ainmntorq/nvs (fig. 62), aud Sarda (fig. 

 32). In the Thunniclai these fius are falcate, amspicuously developed, and 

 interspiuüiis bones suppirting fin-rays of tbese fins are remarkiibly broad. 

 In some Ibrms of Nvothunnua »nacroplerus tbese fins are unnsualh' di;- 

 veloped, brightly coloured, and their tips nearly touch the terminal piints 

 of the caudal. In tunnies as well as iu Gi/bium these fius gradually elongate 

 with the ago of the fish. In immature tunnies and also in Ixjuitos the 

 second doraal and anal are smaller than the first dosml (figs. 43, 53-56). 

 These fins are very small in the Katsuwom'da^, especially in the degenerated 

 genera, Euthynnus and Aims. 



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 ScombridaB 

 the fin-rays are soft, thin, and transversely articulated. Iu the Cybiidso 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 oa60'^ 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 

 Thunnidaj the fin-mj^ of the caudal are so thick and robust, that prehistoric 

 fishermen apparently used it for spear-heads. A specimen of such an im- 

 plement 21 cm. long, carved from one of these fin-rays oi our common tunny, 

 was discovered by Mr. Genshichi Yendo in a shell-momid 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 Thunnidaa and Katsuwonid». 

 Fin-rays of the caudal of the striped bonito are sometimes used as to(jth-picks 

 after being cleaned and bleachetl. Among the so-called scombroid fishes in 

 oiu: waters the caudal fin is largest in Cyhium chinense, the length of its upjoer 

 lobe being longer than the height of the body, and ca. 1/4 the length of the 

 body (fig. 34). In Cybnm gvtlatum (fig. 61) the caudixl fin is also very large. 



SKELETON. 



The Scombridae, CybiidiP, and Plecostoi differ a groat deal from each 

 other in the skeleton, the fundamental structure of the IxxJy. There seems to 

 be very little relation between the skeleton of the Scombridae and that of the 

 Cybiida? ; but the gradual Iransformation of the skeleton of the Cybiida) to 



