roMVAiiATivi: sTi'DV OK scoMiiKoir) I'MrKs. 325 



connecting the anterior and jxjsterior angles are strengthened Iiy tliick 

 ridges. In the Soombridaj the oi^ercle is thin, rather uaiTow, and the lower 

 angle is acute, while the upper and posterior angks ai'c rounded. The dorsal 

 posterior side has an indentation just above the jxisterior angle. Hie dorsal 

 ]X)rtion i. e. the pn-tion above the horizontal diagonal is snaailer than the 

 ventral portion. Tlie articular cup is more or less romided with a sliarp tjotli 

 at the anterior dorsal uiargin. In tlie Cybiidaj the opercle is rather broad, 

 and more or less iJentagoual. The dorsal portion is smaller and thinner than 

 the ventral. The dorsal angle is roimdixl, and the posterior sides are more 

 or less seiTatcd. The ventral anterior side is not sti-aight. Tlie articular cup 

 is narrow and elongate. In the Plccostci the opercle is tliin but firm, and 

 nearl)- quadrate in form, so that the dorsal and ventral portions are neaily 

 equal to each other. Tlie dorsal anterior side is concave. Tlie articular cnp 

 is ellipsoidal. 



The suboperde is more or less triangular, its upper side being overlap^x^d 

 by tlie oi^ercle, and the anterior side by the interopercle, while the posterior 

 side remains free. lu the Scombridso the subopercle is very narrow, and 

 bifurcated at the dorsiil end. The anterior branch is short and pointed. In 

 the Cybiidae the bone is broad, its anterior branch is also broad and some- 

 times two-homed, except in Sarda and Gymnosarda. In the Tlumuidse the 

 anterior branch is abortive and the whole bone is netu-ly obovate. In Thunnns 

 orienlalis and also in Th. thynnus of the Altantic, the subopercle is more or 

 less crenulated or concave at the anterior margin ; but in other tunnies the 

 anterior margin of tlu; suboi»rcle is convex. In the KatsuwonidsB the anterior 

 branch is produced auteriorly and nearly horizontally, ending with a blunt 

 end. 



The interopercle is an ovate bone, forming the ventral free margin of the 

 giU-cover with fine serratiu-e. The bone is connected by a hgament to the 

 posterior end of the hyoid arch. The interopercle of TImmws orientalis Ims 

 its posterior margin convex, while that of the other Japinese timnies k« its 

 posterior mai'gin nearly- sti'aight. 



The preopercle is a lai-ge bent bone, of which the vertical limb fits 

 closely figainst a groove of the outer nuirgiu of the hyomandibulai', and the 

 horizontal limb to the metapterygoid and quiwJiate. In the Scombridie this 



