NO. 3539 HARIMERHEAD SHARKS GILBERT 29 



length of snout from one-third to one-fourth of head width; greatest 

 transverse distance between corners of mouth about one-foiu-th of 

 gi-eatest width of head; symphysis of jaws situated posterior to a trans- 

 verse Une drawn between posterior margins of orbits; labial fuiTows 

 absent. 



Origin of first dorsal fin above axil of pectoral fin, a perpendicular 

 line drawn ventrally from origin intersecting at, or slightly behind, 

 this point; first dorsal fin tall, slender, and pointing strongly posteri- 

 orly, a line drawn perpendicularly from apex of fin passing well back 

 of fin lobe; base of first dorsal fin slightly less than one-half head 

 length and almost twice length of pectoral fin base; anterior margin 

 of first dorsal fin broadly cm'ved (excessively cm-ved in embryonic 

 and early post-embryonic individuals) ; upper two-thirds of distal 

 margin of first dorsal fin straight or slightly falcate toward tip, the 

 lower one-third distinctly falcate; lobe of fu'st dorsal fin about one- 

 third length of base; origin of second dorsal fin situated slightly behind 

 origin of anal fin; second dorsal fin base slightly greater than foiu-- 

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

 longer than one-half length of head and a little less than greatest 

 vertical height of first dorsal fin; pectoral fin two-thirds as broad as 

 long; pectoral fin base about four-fifths length of anal fin base; 

 anterior margin of pectoral broadly rounded (strongly curved in 

 embryos and early post-embryos) ; distal margin of pectoral broadly 

 falcate; apex of pectoral broadly pointed; inner corner of pectoral 

 broadly rounded; length of pelvic fin almost equal to length of anal fin; 

 pelvic fin base slightly less than length of anal base; anterior margin 

 of pelvic nearly straight, except near apex, where it is broadly curved; 

 length of anal fin slightly greater than length of pelvic fin; anal fin 

 base slightly (up to one-sixth) longer than pectoral, pelvic, and second 

 dorsal fin bases; anal fin deeply falcate toward apex, nearly straight 

 toward tip of lobe; length of caudal fin nearly a third of TL; upper 

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

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

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

 lobe of caudal narrow and long, the distance from angle included by 

 the upper and lower caudal lobes to tip of latter going about 23^ 

 times in anterior margin of lower caudal lobe; 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 45° angle from a perpendicular 

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

 margin of lower caudal lobe nearly straight or slightly concave. 



Anterior margin of rostral node of chondrocranium straight; 

 accessory rostral cartilages absent; anterior fontanelle (viewed 

 ventrally) shallow and nearly straight on posterior margin; prominent. 



