320 KaMAKICHI KISHINOUYE : 



at the dorsal margin to fit to a latersil ventral process of the prefrontal. The 

 dorsal margin of these bones is rather .thick, but the ventral margin is very 

 thin. These bones protect the lower side of the eyes. 



The suborbital ring of bones is more or Jess conspicuous in the Scombridae, 

 but in the other groups of the so-called scombroid fishes the ring is inconspicuous, 

 as the bones of the ring are not much differentiated from scales on the cheek. 



Jaw Bones. 



In the Scombroid fishes the promasillary is a long, curved bone, with a 

 long thick head. The bone becomes gradually narrow behind, and without 

 any marked prominence or groove. In the Scombridae the bone is very thin, 

 slender, and its head is low and blunt. In the Cybiidse it is massive, and 

 its head is also low. In that family in general the anterior end of the 

 premaxillary is sharply pointed and the dorsal tip of ite head is oblique and 

 pointed. In the Plecostei the anterior head of the premaxilliiry is large, 

 blunt, and thick, while the remaining part is laterally compressed, and 

 compai'atively narrow. 



The maxillary is also a long, curved bone with a thick hollow head, lying 

 ou the premaxillary. The shaft of the bone is thin and naiTow at the 

 posterior end, but thick and grooved at the anterior part. In the Scombridi» 

 tlie maxillai-y difi'ers gi'eatly from tkat of tlie other scombroid fishes. The 

 head is small, its excavation shallow, while the shaft is uniform!}- flat and 

 broad, and has an indentation at the posterior ventral margin. The dorsal as 

 well as the ventral margins of the bone are trenchant. In the other scombroid 

 fishes the dorsal margin of the maxillary is generally rounded. In the Cybiidas 

 the head of the maxillary is generally low, grooved at the venti-al side for the 

 greater pai't, and the posterior end of the shaft is broad and flattened. In 

 the Plecostei the • maxillary has the head thicker and larger, and the dorsal 

 margin of the shaft is trenchant in the middle, the ventral margin more or 

 less grooved. The auxiliarv' bone to the maxillary, called jugal by MAsrau- 

 .■\rAN, is very small, naiTow, and insignificant in the Scombrida) ; but in the 

 other families of the scombroid fishes it is comparatively Lxrge and bnjad. It 

 is ix)inted at the anterior end and attached to the dorsal posterior corner of 

 the maxillarv. 



