NO. 3639 HAMMERHEAD SHARKS GILBERT 23 



situated posterior to a transverse line drawn between posterior margin 

 of orbits; labial furrows absent. 



Origin of first dorsal jEin above or slightly anterior to axil of pectoral 

 fin, a perpendicular line drawn ventrally from origin usually inter- 

 secting axil; fifth gUl slit situated distinctly behind, and fourth gill 

 slit above (or very slightly posterior to) insertion of pectoral fin; 

 posterior lobe of first dorsal fin terminating well anterior to insertion 

 of pelvic fin; fu'st through fourth gill slits nearly equal in length, and 

 all longer than fifth gill slit; first dorsal fin relatively slender, not 

 perfectly erect, a line drawn perpendicularly from apex of fin inter- 

 secting free rear margin of fin (posterior lobe) about halfway along its 

 length; base of first dorsal fin about three-fifths head length and 

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

 fin nearly straight, slightly curved near apex; upper half of distal 

 margin of first dorsal fin straight, the lower half falcate; lobe of first 

 dorsal fin (free posterior margin) slightly less than one-half length of 

 base; origm of second dorsal fin situated over posterior third of anal 

 base; second dorsal fin moderately tall, its greatest height five-eighths 

 to five-sevenths as long as base, and about five-sevenths greatest 

 lieight of anal fin; second dorsal fin base about fovir-sevenths length of 

 anal base; lobe of second dorsal fin long, its length about twice greatest 

 height of fin, and extending ahnost to upper precaudal pit; anterior 

 margin of pectoral fin three-fourths to four-fifths length of head, and 

 about equal to greatest height of first dorsal; pectoral fin about three- 

 fifths as broad as long; pectoral fin base four-fifths to seven-eighths 

 length of anal fin base; anterior margin of pectoral slightly convex; 

 distal margin of pectoral slightly falcate; apex of pectoral pointed; 

 inner corner of pectoral narrowly rounded; pelvic fin about five-sLxths 

 length of anal fin; anal fin base slightly longer than pectoral and pelvic 

 bases and more than 1}^ times as long as second dorsal fin base; height 

 of anal fin about two-sevenths again as much as height of second 

 dorsal fin; anal fin deeply falcate toward apex and nearly straight 

 toward tip of lobe; length of caudal fin about one-thu'd of TL; upper 

 margin of caudal slightly convex; terminal part of caudal about two- 

 ninths of total length of fin; posterior margin of terminal part of caudal 

 fin shallowly falcate; terminal apex of caudal broadly pointed; lower 

 lobe of caudal moderately narrow and short; length of lower caudal 

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

 not erect, sloping posteriorly at about a 35° angle from a perpendicular 

 to the body axis; anterior margin of lower caudal lobe convex; posterior 

 margin of lower caudal lobe nearly straight; lower precaudal pit 

 absent. 



Anterior margin of rostral node of chondrocranium straight; acces- 

 sory rostral cartilages absent; anterior fontanelle (viewed ventrally) 



