NO. 3539 HAMMERHEAD SHARKS GILBERT 35 



scallops present on anterior margin of bead, about halfway between 

 nares and tip of snout; outer posterior corner of lateral expansion of 

 head posterior to corner of mouth, probably in specimens of all sizes ; 

 narial flap broad, moderately pointed at tip, with the outer edge 

 curving evenly inward; orbit large, the horizontal diameter about 

 equal to length of longest (second) gill slit; length of snout from one- 

 fifth to one-fourth of head width; greatest transverse distance be- 

 tween corners of mouth from one-fifth to one-foui'th of greatest width 

 of head; symphysis of jaws situated posterior to a transverse line 

 drawn between posterior margins of orbits in specimens of all sizes; 

 labial fiu-row present at corners of lower jaw only (concealed when 

 mouth is closed), about one-fifth as long as greatest horizontal 

 diameter of eye. 



Origin of fii'st dorsal fin above posterior axil of pectoral fin, a per- 

 pendicular line drawn ventrally from origin intersecting axil; first 

 dorsal fin broad, rather erect (not as erect as in large examples of 

 Sphyrna tudes), a line drawn perpendicularly from apex of fin passing 

 close behind base; base of first dorsal fin from two-fifths to nine- 

 twentieths of length of head, and from three-fourths again to nearly 

 twice length of pectoral fin base; anterior margin of first dorsal fin 

 evenly cm-ved, with the part nearest the apex very strongly curved; 

 distal margin of first dorsal fin strongly falcate; lobe of first dorsal fin 

 about one-thii'd length of base; origin of second dorsal fin situated 

 about halfway back above base of anal fin; second dorsal fin base from 

 three-fifths to four-fifths length of anal fin base; anterior margin of 

 pectoral fin from one-half to two-thirds length of head (higher values 

 usually apply to larger individuals) and about equal to or slightly 

 greater than greatest vertical height of first dorsal fin; pectoral fin 

 about two-thirds as broad as long; anterior margin of pectoral moder- 

 ately convex; distal margin of pectoral slightly falcate; apex and inner 

 corner of pectoral rounded ; length of pelvic fin about foiu--fif ths length 

 of anal fin; length of pelvic fin base approximately equal to length of 

 anal fin base; anterior margin of pelvic fin weakly convex, the distal 

 margin nearly straight; length of anal fin equal to or slightly greater 

 than length of pelvic fin; height of anal fin about a third again as much 

 as height of second dorsal; length of caudal fin nearly a third of TL; 

 upper margin of caudal fin nearly straight; terminal part of caudal 

 about one-fifth of total length of fin; posterior margin of terminal part 

 of caudal fin moderately falcate; terminal apex of caudal narrowly 

 rounded ; lower lobe of caudal relatively narrow and long, the distance 

 from angle included by upper and lower caudal lobes to tip of latter 

 going about twice in anterior margin of lower caudal lobe; length of 

 lower caudal lobe one-third to two-fifths as long as upper lobe; lower 

 caudal fairly erect, sloping posteriorly at about a 35° angle from a 



