COMPARATIVK STUDY OF St^OMHKOID FISHES. :>07 



fisliormeii call tiie nlbaeore " tomlw-slilbi ", incixniup; the diMgon-tly tunny. Tiie 

 iiniulwr of fiu-rfty.s iu the pectoral is 18 iu the pienus Scomber, 19-24 in the 

 geung Gtihium, 25 in Gijmnosard.', 30-36 in the Thuunidne, ca 30 in 

 KatHuwonus and Evthynnus, and ca 25 iu Auxis. Thus in general the number 

 of fin-rays in the pectoral increases as the struetm'e of the body becomes more 

 complicate, and again decreases iis the structure degenerates. The eximnse of 

 the ppctoral is nearly unchanged, though the number of rays is increased. 

 Tlicre is no doubt that the greater numlier of fin-rays increases the rigidity 

 oi the fin itself. In the Scombrid» the pectorals are small, ti'iangular, and 

 ai'e situated a little higher than in the Cybiidaj and Plecostei. In the 

 Cybiida? the pectorals are also small, often broad at the origin, and more or 

 less ci-enulated at the venti-al mm-gin, as iu (J/jhiinn niphonium, C. rjutMura 

 and Gymnosarda nuda. In Cyhium cJdneme, however, the pectorals are large, 

 and roimded at the posterior mai'giu (fig. 34). The form is finite exti-a- 

 ordinaiy. In the Thunnidje the pectoi^als are generally long, reaching the 

 origin of the second dorsal, and even pas? lieyond it. These fins gi'adually 

 tapering behind, are sabre-shaped. In the Katsuwonidre the pectorals are 

 small and ti-iangular. Tliey iU'o pointed at the x)osterior doi-sal end. In 

 Surda and Plecostei a sjiecial elastic p-otuberance or rather a ridge is 

 developed at the inner or dorsal side of the root of pectorals to fit tightly to 

 a conesponding gi'oove on each side of the body. 



The venti'als are thoracic, moderate iu size, alwaA's composed of one 

 spine and five fin-rays, and as iu luauy other fishes fit to depressions of the 

 body when folded. These fins seem to be of secondaiy importance, as their 

 fin-rays remain transversely aiiienlated, and they ai-e reduced in size in the 

 Cybiidie, Ix'ing smaller than the anjtl, except in the genus Gymnosarda. 



The dorsal is divided into two, fii-st and second, and the posterior portion 

 of the latter is fiuiher divided into many fiulels. In the Scombridse the 

 number of finlets is generally 5, in the Cybiidae 6-9, and in the Plecostei 

 8 or 9. The fii'st dorsal Ls never continuous with the second, and is formed 

 of several spkies which when depressed are whoU}' received in a gi'oove. The 

 tip of the spines of the fii'st doi"sal is flexible, and each spine has a hole at 

 the proximal end. In the Scombridse and also iu the genus Auxis of the 

 Katsuwouidsp, tlie two dorsals aie sejjarated by an interspace from the 



