NO. 3539 HAMMERHEAD SHARKS — GILBERT 49 



from the angle included by the upper and lower caudal lobes to 

 tip of latter going from 2 to 2^ times in anterior margin of lower 

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

 as upper lobe; lower caudal lobe sloping posteriorly at about a 45° 

 angle from a perpendicular to the body axis; anterior margin of 

 lower caudal lobe weakly convex; posterior margin of lower caudal 

 lobe nearly straight. 



Anterior margin of rostral node of chondrocranium either straight 

 or with a poorly defined indentation; accessory rostral cartilages 

 absent; rostral fenestra absent; anterior fontanelle (viewed ventraUy) 

 appearing broad and shallowly U-shaped, with a distinct, rounded, 

 median notch; prominent pointed wings present on sides of rostral 

 node; anterior wing of olfactory cartilage prominent, pointed, and 

 projecting medially; anterior part of preorbital process short and 

 rather blunt, with a moderately sharp angle on anterior edge; pos- 

 terior part of preorbital process terminating in a knob, the anterior 

 corner of which is evenly rounded and projects forward, and the 

 posterior corner of which is somewhat more angulate (pis. 7 a, b) . 



Total number of vertebrae 142 to 172 (seven specimens examined); 



body vertebrae 71 to 88, the relative number of body to caudal 



vertebrae varying from 9 more to 2 less. 



_ . 12 to 14-0 or 1-12 to 14 ^ . ^ , n , , ,u 



Teeth ; teeth not serrate; first upper tooth 



12 to 14-1-12 to 14 ' ' ^^ 



erect and symmetrical, but subsequent upper teeth becoming in- 

 creasingly oblique toward corners of mouth; teeth 3 through 10 or 

 11 largest in both jaws; cusps evident only on teeth 1 through 9 in 

 specimens examined (through 11 or 12 according to Bigelow and 

 Schroeder, 1948, p. 423); lower teeth shorter than upper teeth, with 

 narrower cusps and slightly broader bases, the first through third 

 teeth erect and symmetrical, the fourth through seventh or eighth 

 slightly oblique, the eighth and subsequent teeth without cusps or 

 definite cutting edges; three series of teeth functional in front and 

 one or two series functional along side of upper jaw; four to six series 

 functional in front, usually two functional along side, and three 

 functional toward corner of mouth of lower jaw. 



Dermal denticles (examined from upper part of back beneath first 

 dorsal fin) closely overlapping, the blades rather steeply raised; 

 length of denticle (measured to tip of median marginal "tooth") 

 as great, or nearly as great, as width; five strong ridges usually pres- 

 ent, and as many long, sharp-pointed teeth (these teeth are some- 

 times blunted or broken) usually present at posterior margin of 

 denticle, the outer ridges and teeth sometimes rudimentary or absent, 

 particularly in smaller individuals; median tooth on denticle ordi- 

 narily slightly longer than more distal teeth ; pedicel short and slender. 



219-937—67 4 



