HAMMERHEAD SHARKS — GILBERT 



41 



Fraser-Brunner (1950, pp. 213-219) synonymized S. diplana with 

 S. lewini, although he continued to recognize S. oceanica as valid, 

 citing supposed diiferences in size of eye, length of snout, relative 

 position of first dorsal fin, size of second dorsal fin, and shape of head. 

 Examination of specimens from the Gulf of Aden (BMNH 1925.7.20. 

 32.37), which were identified by Fraser-Brunner as S. oceanica, fails 

 to substantiate his conclusion that this nominal species is a valid form. 



Diagnosis. — Characters mentioned in the diagnosis of the subgenus 

 Sphyrna are not repeated here. 



Figure 10. — Sphyrna lewini: a, juvenile female, 639 mm. TL, from Rio de Janeiro, Brazil 

 (MCZ 462); b, ventral view of head; c, upper and lower teeth, left side, about 0.55 X; 

 d, fourth upper tooth; e, twelfth upper tooth;/, third lower tooth; g, eleventh lower tooth; 

 h, dermal denticles, about 42 X . {d-g, about natural size.) (From Bigelow and Schroeder, 

 1948, p. 415.) 



Sphyrna lewini is characterized (as is S. zygaena, its closest relative) 

 by a long second dorsal fin lobe and a low second dorsal fin, the length 

 of the former about twice greatest height of fin. The anterior-median 

 pore patch on the underside of the head is unique, the patch character- 

 ized by a rather sharp, smoothly rounded angle at the outer-posterior 

 comer and by a narrow triangular area, which is devoid of pores, in 

 the median-posterior region (fig. 22d). 



S. lewini is distinguished from S. zygaena by a median indentation 

 (scallop) on anterior margin of head; a shorter inner narial groove, 

 which extends 40 to 45 percent of distance from inner margin of nares 

 to tip of snout; orbit farther from nares, being separated by a distance 

 slightly less than greatest horizontal diameter of eye; tip of second 

 dorsal lobe reaching closer to upper precaudal pit, the lobe extending 

 from three-fourths to four-fifths of distance from second dorsal base 



