very rarely appear specimens with a gill -raker count of 8 - 9 / 18 =■ 20, 

 but not enough study has been done to detemine whether or not it is a 

 different speciesc 



II. SPEARFISHES 



Ao General 



ao External form 



The spearfishes are the fishes belonging to the two families 

 Istiophoridae and Xiphiidaeo 



These fishes are generally large with elongated bodieso 

 The fishes of the family Istiophoridae are more or less markedly 

 flattened laterally, but the Xiphiidae show almost no lateral 

 flatteningo The caudal peduncle does not exhibit the marked 

 abrupt taper of the tunaSj and the keels on the peduncle are 

 two pairs in the Istiophoridae and one pair in the Xiphiidaeo 

 The most remarkable characteristic of these fishes is the pos- 

 session of a long projecting rostrum shaped like a spear or 

 like a double-edged swordc This projecting rostrum is formed 

 mostly by the premaxillary and in the Istiophoridae it is almost 

 solid, but in the Xiphiidae the center is hollow with occasional 

 membrane-like structures like the joints in a bambooo The lower 

 jaw also projects somewhat and its tip is sharpo In the Istio- 

 phoridae there are file=like teeth on both the upper and lower 

 jaws J but no such teeth are developed in the Xiphiidae^ The com^ 

 parative lengths of the jaws differ in the various species^ the 

 ratio being lo28 to 2o21 in the Istiophoridaep with the short-nosed 

 spearfish having the smallest value and the black marlin the 

 largesto In the Xiphiidae the difference is great, amounting 

 to 4o5o The Istiophoridae have slender bony scales on the 

 opercles and covering the whole body, where they are buried in 

 the skin, but the Xiphiidae have no scales, there being only a 

 section of the ventral surface of the pectoral region which 

 feels rough to the toucho A lateral line is present in the 

 Istiophoridae but is lacking in the Xiphiidaeo The dorsal and 

 anal fins each have two separate bases, although in juvenile 

 fish they form a single basoo The pectorals are located low 

 on the body and are well developedo The ventral fins in the 

 Istiophoridae have degenerated into filiform appendages com- 

 posed of three rays firmly joined together, and in the Xiphiidae 

 there is no visible vestige of the ventral finSo There are 

 dermal grooves along the bases of the first and second dorsal 

 fins, and the greater portion of these fins can be folded away 

 into themo There is also a rather conspicuous groove along the 

 center line of the belly from the base of the ventral fins to 

 the neighborhood of the anus, and the ventral fins can be 

 accommodated thereinc The caudal fin is large, and both of 

 its lobes are narrow and widely separatedo If the lengths of 



34 



