3G4 
KAMAKICHI KISHINOUYE: 
free from the isthmus. Iu the Scombridae we find a slight depression at the 
posterior, dorsal margin of the gill-opening, just anterior to the origin of the 
pectoral. This depression together with the soft flappy portion of the opercle 
above it, make easy the escape of foul water from the gill-chamber. In Bastrel - 
liger, moreover, a slight depression or groove is found on the hind ventral mar¬ 
gin of the gill-opening, or at the lower, anterior margin of the shoulder 
girdle. Such structures of the gill-opening as the flappy portion of the opercle 
opposite to the slight depression of the gill-opening, and another depression 
on the posterior ventral margin are often found in fishe3 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 number, and the mem¬ 
branes connecting them are rather wide and extensive. In the Scombridae the 
branchiostegals are dissimilar in breadth aud form, posterior ones becoming 
broader and much more curved or bent. 
In the Cybiidae the branchiostegals are slender, and the membrane connecting 
them is extensile. In the Plecostei the posterior branchiostegals are more or 
less broad, and the free margin of the membrane is much thickened, hence 
tough from the development of connective tissue. The membrane is nonex- 
tensile and remains fastened to the inner side of the opercle, a little removed 
from its margin, like an inner rim of a lid to a base. 
The pseudobranchiae are equally well developed in the Scombridae, 
Cybiidae, and Plecostei. 
The brancliial lamellae are very thin, and closely set, nearly equally in 
all scombroid fishes ; but them length and breadth vary greatly in different fami¬ 
lies. Their length is proportional to the breadth of the opercle. In the Scom¬ 
bridae the gill-lamellae are short and narrow, about half the length of the upper 
arm of the first gill-arch. In the Cybiidae they are a little longer than half 
the length of the upper arm of the first gill-arch, and in the Plecostei they are 
equal in length with the latter. In the Plecostei each branchial filament is 
strengthened on the proximal, axial side of each gill-arch with many minute 
transverse rods. 
In Acanfhocybium the branchial lamellae anastomose with each other as 
in the Xiphiidae, but in the former the anastomosis is limited to the proximal 
portion of the lamellae, not over the whole extent of the gills as in the latter. 
