30 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 124 



way than do the Scombridae. In the Scombridae, the route of forward 

 trajectory seems to be controlled, at least in part, in usual percoid 

 fashion by a combination of well-developed 6-rayed pelvics directly 

 below the highly placed pectoral fins (Harris, 1938). In the istiophorids, 

 xiphiids, and Luvarus, the pelvic fins have a reduced number of rays 

 or none. The pectorals are low on the body and have become fixed 

 in extended position in the adults of Xiphias and of the istiophorid 

 Istiompax indicus (thus secondarily resembling the shark condition). 

 In this regard, it should be noted that, in the trichiurids and in many 

 gempylids, the pectorals are low and the pelvics reduced or absent, 

 but such forms are relatively small, weakly swimming fishes. 



Finally, the dorsal fin of the Scombridae commences well behind 

 the head. That of the Istiophoridae and Xiphiidae originates over 

 the back of the head. The first interneurals of Xiphias are shown by 

 Gregory and Conrad (1937, fig. 3) to extend downward into the 

 region of the skull-vertebrae articulation. In the juvenile Luvarus 

 (Gregory and Conrad, 1943, fig. 38), the dorsal fin again originates 

 far forward, but, with growth, moves back, leaving, however, a pair 

 of large interneurals that interdigitate between the cranium and the 

 first vertebra (Gregory and Conrad, 1943, fig. 8). 



In certain respects, e.g., the 23-26 vertebrae, the Istiophoridae, 

 Xiphiidae, and Luvaridae are more generalized than the Scombridae. 

 That they are specialized scombrid offshoots seems an impossible 

 conclusion, and that they are even related to the Scombridae, an 

 improbable one. 



A more difficult problem is to determine what the Xiphioidei is 

 related to and/or derived from. Before this matter can be profitably 

 discussed, the question arises as to whether or not the Istiophoridae, 

 Xiphiidae, and Luvaridae are interrelated. Regan (1909a), Gregory 

 and Conrad (1937), and others have postulated that the Xiphiidae 

 and Istiophoridae extend back separately into Eocene times. That 

 the two families are related more closely to one another than to any 

 other modern family has not, to my knowledge, been questioned. 



Whether or not the Luvaridae are related to the Istiophoridae and 

 Xiphiidae is more doubtful. Certainly Luvarus has many features 

 that separate it widely from all other living fishes. In mouth and 

 snout structure, Luvarus differs widely from the istiophorids and 

 xiphiids. It may be that these features provide good indications of 

 phylogenetic relationships, but the alternative possibility at least is 

 suggested here that the anterior profiles of Luvurus, on the one hand, 

 and of the istipohorids and xiphiids, on the other, represent alterna- 

 tive attainments of hydrodynamic efficiency in large, strongly swim- 

 ming fishes and, hence, are not necessarily of great phylogenetic 

 significance. In any event, the Luvaridae herein are included pro- 



