o. 3539 HAMMERHEAD SHARKS GILBERT 19 



examined about dy> feet long Sphyrna media Springer 



Eastern Pacific, from Panama to Gulf of California; also in 



southern Caribbean and southwestern Atlantic, from Panama to 



Brazil. 



6b. Distance from tip of snout to symphysis of upper jaw slightly longer, 



usually more than 40 percent of head width (table 8; fig. 16); 



anal fin less deeply falcate, with a more rounded apex (fig. 18a); 



mouth slightly narrower (fig. 18b) ; anterior-median pores on 



ventral surface of head as in figure 22(j; chondrocranium as in 



plate 7d; maximum size possibly smaller, the largest specimen 



examined a little over 2 feet long . . . Sphyrna corona Springer 



Eastern Pacific, from Colombia to southern Mexico. 



2b. Anal fin and base shorter, former measuring from 8.2 to 10 percent, and 



latter from 3.8 to 6.7 percent of total body length; fifth gill slit shorter 



than first gill slit (fourth gill slit about as long as first gill slit) ; fifth gill 



slit situated behind insertion of pectoral fin; orbit larger, its horizontal 



diameter greater than shortest distance from anterior edge of orbit to outer 



margin of narial opening; teeth broad, not needle-like in appearance; lower 



precaudal pit absent; posterior lobe of first dorsal fin not extending to 



above insertion of pelvic fin; maximum size larger, some individuals 



reaching 20 feet TL 7 



7a. Inner narial groove absent; pelvic fin falcate; second dorsal fin higher, 

 length of its anterior margin greater than length of anterior margin of 

 anal fin; lobe of second dorsal fin shorter, not extending nearly to 

 caudal pit, and, when extended vertically upward, about equal to 

 greatest height of fin; teeth strongly serrate, even in small individuals; 

 anterior- median pores on ventral surface of head as in figure 226; 

 chondrocranium as in plate 6a ... . Sphyrna mokarran (Riippell) 

 Circumtropical in distribution, but apparently absent from the more 

 isolated oceanic islands. 

 7b, Inner narial groove present; pelvic fin not falcate; second dorsal fin 

 lower, length of its anterior margin less than length of anterior margin 

 of anal fin; lobe of second dorsal fin longer, extending nearly to caudal 

 pit, and, when extended vertically upward, definitely exceeding greatest 

 height of fin; teeth smooth in small individuals, often weakly serrate 

 in large individuals; anterior- median pores on ventral surface of head 



not as in figure 226; chondrocranium not as in plate 6a 8 



8a. Median notch absent from anterior margin of head; inner narial groove 

 extending at least halfway from narial opening to median part of 

 anterior margin of head; base of anal fin shorter, about equal in 

 length to base of second dorsal fin and slightly less than base of 

 pectoral fin; rostral fenestra ordinarily absent; anterior-median 

 pores on ventral surface of head as in figure 22c; chondrocranium as 

 in plate 6c. 



Sphyrna zygaena (Linnaeus) 

 Antitropical in distribution; occurring in cooler waters of northern 

 and southern hemispheres, but absent from intervening tropical 

 waters. 

 8b. Median notch present on anterior margin of head; inner narial groove 

 not extending halfway from narial opening to median part of anterior 

 margin of head; base of anal fin longer, greater in length than 



