TtEPORT ON THE PET AGIO FISHES. 17 



Thynnus thunnina (C. V.), yoiinii- (T'l. 11. fig. D). 



Dr. Liitkeii ' has figuied two very young Scombroid fishes which he considers to be 

 the, young of Orcijnus germo. A similar specimen 17 mm. long was obtained in the 

 surface-net on the passage from the Admiralty Islands to Japan ; it is, however, 

 sufficiently different to prove its specific distinctness from the specimens figured by 

 Dr. Liitken. All three specimens have a more or less extended black patch on the 

 spinous dorsal, a feature which is commonly preserved in adult specimens of the genus 

 Cyhium, but which is much more rare in mature examples of Thynnus. I have seen it 

 in the type specimen of Thynnus affinis of Cantor, from Penang, which is in fact 

 specifically identical witli Thynnus thunnina. Although I provisionally identify our 

 young example witli this latter species, I consider it quite possible that all these young 

 specimens may belong to Cyhium. Perhaps the young of two genera .so closely allied as 

 Thynnus and Cyhium are not readily distinguishable. 



Our young .specimen is uniformly silvery, with the exception of the black patch which 

 covers the first part of the first dorsal fin. Its body and tail are covered with minute 

 scales which become visible when the surface of the specimen is allowed to dry. The 

 head is large, at least one-third as long as the entire fish, the caudal fin included. Eye 

 large, about two-sevenths of the length of the head ; jaws armed with the strong teeth 

 which are characteristic of the genus. Angle of the praioperculum armed with two 

 stronger spines which are followed by smaller ones along the lower margin. The 

 anterior part of the s2">inous dorsal fin is lower than in the fishes figured by Liitken, 

 the posterior portion very low and continuous with the soft dorsal fin; there are 

 altogether seventeen spines of which one would belong to the soft portion. All the 

 rays of the soft dorsal fin, nineteen in number, are connected by membrane, but the 

 seven or eight last are already sufficiently differentiated to show that they would have 

 been modified into finlets. The anal fin is very similar to the second dorsal, consisting 

 of twenty-three rays, of which the two or three anterior would have been converted into 

 spines ; the other anterior rays are very closely set, whilst the eight last arc further apart 

 and evidently finlets. The pectoral and ventral fins do not show any peculiarity. 

 Caudal fin excised, the middle rays being quite free and not covered with scaleless skin 

 as in the adult Thynnus. The trunk of the tail is very thin and depressed, provided on 

 each side with the characteristic pair of keels, which prevents me from referring this 

 specimen to the genus Cyhium. 



1 Vidensk. Sekk. Skriv., xii., 1880, pi. iii. ti^-s. 1, ± 



(ZOOL CnALI.. RXP. — PART T.xxviir. — 1 f'SO. ^ liii 3 



