no. 3647 PERCIFORM FISHES — GOSLINE 29 



imperialis, has been allocated variously; Regan (1903a, p. 372) 

 considered it "a most abnormal and specialized Scombroid." 



A principal reason why Regan (1903a; 1909a) placed Luvarus 

 among the scombroids seems to have been that in it, as in the Scom- 

 bridae and Xiphiidae, "the deeply forked bases of the rays of the 

 caudal fin are inserted nearly vertically and extend over the hypural 

 so as to almost entirely conceal that bone, those of the upper and 

 lower series nearly meeting in the middle line on each side" (1903a, 

 p. 372). Additionally, in Luvarus, "the ossified sclerotic and broad 

 opercular bones are typically Scombroid features" (1903a, p. 374). 



In the Xiphiidae and Istiophoridae, along with the peculiar caudal 

 ray bases noted above, the rostral structure has been considered a 

 morphological extrapolation of the type found in the scombrids in 

 general, most notably in Acanthocybium (cf. fig. in Regan, 1909a). 



To the present author, it seems that all of the morphological features 

 mentioned above may well be merely adjustments of large, power- 

 fully swimming fishes to the requirements of hydrodynamic efficiency. 

 (Hertel, 1966, e.g., p. 255, stresses the difference in what constitutes 

 hydrodynamic efficiency in large, powerfully swimming animals and 

 in small, weak swimmers.) With increase of body size and swimming 

 speed, the role of hydrodynamic forces in the existence of the animal 

 becomes, of course, increasingly important. It is probably significant 

 that among the members of the percoid family Carangidae, which 

 also contains large, powerful swimmers, almost all of the morphological 

 characters discussed above have been duplicated. Another, at least 

 curious, parallel in the Carangidae is that, in those forms with a high, 

 blunt head, the premaxillary remains protrusile, as in Luvarus; 

 however, in the pointed-headed Chorineminae (Suzuki, 1962, p. 147), 

 the premaxillaries are rigid and form a beaklike structure similar to 

 that of Scomber. 



If, however, one excludes from consideration those features that may 

 be related to hydrodynamic efficiency, there seems to be slight re- 

 semblance between the Istiophoridae, Xiphiidae, and Luvaridae on 

 the one hand, and the Scombridae, on the other. In the former group, 

 the vertebrae number from 23 to 26 (a typically percoid condition); 

 in the Scombridae, the vertebrae are 30 or more. In Xiphias and 

 Tetrapterus (Gregory and Conrad, 1937, fig. 5), the caudal skeleton 

 is only about as specialized as that of Scomber, certainly far less 

 modified than the caudal skeleton of the tunas. In Luvarus, with the 

 fusion of the last two vertebrae, the caudal skeleton (Gregory and 

 Conrad, 1943, fig. 7) has become modified in a different fashion than 

 that of the Scombridae. 



Probably of greater importance, the istiophorids Xiphias and 

 Luvarus seem to guide then forward trajectory in a somewhat different 



