FISHES. 



203 



their culmination in forms that are now so isolated by reason of the loss of interme- 

 diate types that they are distinguished as peculiar families. Among the Scombrids in 

 question is the genus Acanthocybium, which exhibits, in its elongated spinous dorsal 

 fin, and projecting jaws, as well as the structure of the gills, characters which tend 

 towards the sword-fishes. Another specialized group is that represented by the elon- 

 gated compressed species in which the spinous dorsal is also elongated, and in which 

 the ventral fins become feeble or obsolescent. These lead naturally to another group 

 of fishes which apparently are worthy of differentiation into two distinct families. 

 First, we may consider the sword-fishes, and afterwards the ribbon-like Scombroidea. 



The Scombroidea with the upper jaw elongated and condensed into a sword-like 

 weapon have generally been combined in one family, but the differences manifested 

 by the species are so great as to demand a recognition of two distinct families, the 

 Histiophoridse and the Xiphiidse. 



The sail-fishes or bill-fishes, constituting the family Histiophoeid^, have the body 

 elongated and more or less compressed ; the spinous dorsal fin is very long and per- 

 sistent, and often greatly developed, the spines being elongated, connected by mem- 

 brane, and constituting the sail of the fishermen, and the ventral fins are present in 

 the shape of elongated compressed spines, and generally have one or two axillary 

 rays ; but the chief differences are exhibited by the skeleton, prominent among which 

 are the elongated hour-glass-shaped vertebras, flag-like neural and haemal spines, 

 and the well-developed ribs. 

 Two distinct genera are rep- 

 resented in the American seas. 

 The spear-fish or bill-fish, Tet- 

 rapturtis albidus, is a form 

 having the dorsal fin low or 

 moderately developed, and the 

 ventral fins are represented 

 only by the spines. It is an inhabitant of the American seas as far north as the 

 New England waters in the summer months, and is not rarely taken by those 

 engaged in the sword-fishery. Occasionally, also, they enter into the fish-pounds 

 along the coast. In the tropical waters, however, the horizon of the species, according 

 to Professor Poey, is at a depth of about a hundred fathoms. It is probable, then, 

 that the temperature guides their movements, and that it is an inhabitant rather of 

 the cooler waters than of the true tropical ones. It is noted for its antagonism to 

 sharks, and the fish is said to become furious at their aj)pearance, and to engage in 

 violent combats with thetn. 



The sail-fish, Iliatiophorus americanus., is scarcely distinct from the H. gladhcs, 

 but is distinguished from the Tetraptitri by the greatly elevated spinous dorsal fin, and 

 by the development of two or three rays within the axils of the ventral spines. This 

 species is also a summer inhabitant of the American waters as far north as New Eng- 

 land, and is likewise occasionally taken by the fishermen. It is, however, so active in 

 its movements that its value scarcely compensates for its capture. 



The true sword-fish is the only representative of the family Xiphiid^. The body 

 is shorter, much stouter, and less compressed than in the Histiophoridae, the spin- 

 ous dorsal becomes atrophied behind, the posterior spines being scarcely visible, 

 and ventrals are entirely wanting. But it is more especially distinguished by the 

 larger short vertebrae, the spiniform neural and haemal spines, and the development 



Fig. 116.— Hlstiophorus gladius, sail-flsb, young. 



