3(34 KAMAKICm KISmNOüTE: 



free from tlie istbmiis. In the Scombiidae we find a slight depression at the 

 ]josterior, dorsal margin of the gill-opening, just anterior to the origin of the 

 pectoral. Tliis depression together with the soft flappy portion of the opercle 

 above it, make easy the escape of foiü water from the gill-chamber. In Bastrel- 

 liyer, moreover, a sUght depression or groove is found on the hind ventral mar- 

 gin of the gill-opening, or at the lower, anterior margin of the shoulder 

 gii'dle. Such structm'es of the gill-opening as the flappy portion of the opercle 

 opposite to the slight depression of the gill-o^jening, and another depression 

 on the posterior ventral margin are often found in fishes of the Carangidae as 

 well, and we see that there is some relation between these two families. 



The branchiostegals are slender, seven or eight in nmnber, and the mem- 

 branes connecting them are rather wide and extensive. In the Scombridae the 

 bi'anchiostegals are dissimilar in breadth and form, posterior ones becoming 

 broader and much more cm'ved or bent. 



In the Cybüdae the brancliiostegals are slender, and the membrane connecting 

 them is extensile. In the Plecostei the posterior branchiostegals are more or 

 less broad, and tlie free margin of the membrane is much thickened, hence 

 tough fr"om the development of connective tissue. The membrane is nonex- 

 tensüe and remains fastened to the inner side of the opercle, a little removed 

 fr'om its margin, hke an inner rim of a lid to a base. 



The pseiidobranchiae are equally well developed in the Scombridae, 

 Cybiidae, and Plecostei. 



The brancliial lamellae ai'e very thin, and closely set, neai'ly equally in 

 all scombroid fishes ; but thefr length and breadth vai'y gi'eatly in diflfereut fauii- 

 hes. Thefr length is projxjiiional to the breadth of the opercle. In the Scom- 

 bridae the gill-lamellae arc short and uaiTow, about hiilf tlie length of the up^^er 

 ai'm of the first gill-ai-ch. In the Cybiidae they are a httle longer than half 

 the length of the upper m-m of the fii'st gill-arch, and in the Plecostei they are 

 equal in length with the latter. In the Plecostei each brancliial filament is 

 sti'engthened on the proximal, axial side of each gill-arch with m;iny minute 

 transverse rods. 



In Acanihocyhium the branchial lamellae anastomose with ejvch other as 

 in the Xiphiidae, but in the former the iuiiistomosis is limited to the proximal 

 portion of the lamellae, not over the whole extent of the gills as in the latter. 



