2726 THE BONY FISHES AND GANOIDS 



Rome were in the habit of presenting the head, which was considered the finest 

 part as a sort of tribute to the three local magistrates who acted for the time as the 

 conservators of the city." It is certain members of this genus that have taken to 

 a fresh-water existence. 



THE SWORDFISHES Family X 



With this small and well-defined family, all the members of which attain very 

 large dimensions, we come to our first representatives of purely pelagic fishes. 

 Sufficiently distinguished from all their allies by the production of the upper jaw 

 into the long, wedge-shaped, sword-like weapon from which they take their name, 

 the swordfishes are further characterized by the elongate and compressed body, the 

 laterally-placed eyes, and the deep cleft of the mouth. Teeth are either absent or 

 rudimentary, and scales are likewise wanting, or represented merely by small rudi- 

 mental structures. The dorsal fin is either single or divided, but has no distinct 

 spinous portion, and the pelvis, if present at all, takes the form of long, rod-like, 

 thoracically-situated appendages. There are seven branchiostegal rays, and an air 

 bladder is present. In the adult the sword is formed by the coalescence of the pre- 

 maxillae, vomer, and ethmoid, and is rough on the under surface from the presence 

 of rudimental teeth. The swordfishes are divided into the genera Xiphias and 

 Histiophorus, according to the absence or presence of pelvic fins; these appendages 

 in the latter being in the form of from one to three rays. There is considerable 

 variation in the height of the dorsal fin, which is frequently so lofty as to project 

 some distance above the water when the fish is swimming near the surface, and 

 even, it is said, to answer the purpose of a sail. In the young, this fin is much 

 higher in proportion to the length of the body than it is in the adult. In very 

 young examples of the typical genus the beak is comparatively long, there are 

 conical prominences on the edge of the supraorbital, the occiput is devoid of a spine, 

 and there are two short, tooth-like processes at the angle of the preopercular. In 

 Histiophorus, on the other hand, the beak at a corresponding age is much shorter; 

 the supraorbital edge is finely denticulated, or smooth, and there is a bony spine on 

 each side of the occiput and at the angle of the preopercular. Although they are fre- 

 quently not more than four to six feet in length, swordfishes may measure as much 

 as from twelve to fifteen feet, and the sword itself may exceed a yard in length. 

 The common European swordfish {Xiphias gladius), which is occasionally taken on 

 the British coasts, ranges from the European seas to the opposite side of the Atlantic; 

 while to the southward it occurs off the northern and western coasts of Africa. 

 Histiophorus, on the other hand, seems to be confined to the Pacific and Indian 

 Oceans, ranging eastward to Japan. Of the three Indian species, the spotted Indian 

 swordfish (H. gladius] is distinguished by the dorsal fin being much higher than 

 the body, and marked with dark blue spots on a lighter ground of the same color; 

 the body being bluish gray above, and lighter beneath. On the other hand, in the 

 black-finned swordfish (H. immacidatus) the general color of the body is dull gray, 

 and the dorsal and anal fins are blackish. The third species {H. brevirostris} has 



