30 PROCEEDINGS OF THE NATIONAL MUSEUM vol. u9 



broad, bluntly rounded wings present on sides of rostral node; no 

 anterior wing on olfactory cartilage; tip of anterior part of preorbital 

 process very short, blunt, and rather thick; posterior part of pre- 

 orbital process terminating in an evenly rounded knob. 



Total number of vertebrae 205 to 206 (in two specimens examined) ; 

 body vertebrae 95 to 98, there being from 10 to 11 fewer body than 

 caudal vertebrae. 



Teeth ; upper teeth triangidar, on expanded 



16 or 17-1 to 3-16 or 17 ^^ & > f 



bases, the first tooth erect, symmetrical, but the subsequent upper 

 teeth increasingly oblique toward corners of mouth; second to tenth 

 or eleventh teeth the largest in both upper and lower jaws; outer- 

 most teeth in both jaws with distinct cusps; one or two series of teeth 

 functional in alternating rows along sides of upper jaw and usually 

 two rows along sides of lower jaw. 



Dermal denticles (examined from upper part of back beneath first 

 dorsal fin) evenly and closely spaced, but with skin often visible in 

 between, the blades thin and little arched ; length of denticle (measured 

 to tip of median marginal "tooth") about same as width; small 

 specimens with from three to five, larger specimens with five or 

 even six, smooth-topped ridges, and as many short, broadly pointed 

 marginal teeth on dermal denticle; median tooth on denticle slightly 

 longer than more distal teeth ; pedicel short and thick. 



Individuals with gray or grayish brown dorsally, becoming more 

 pale below; no markings on fins. 



Maximum total length reputedly about 20 feet. 



Variation.— Comparatively few specimens of Sphyrna mokarran 

 were available for study, and of these a large percentage (including 

 all individuals from the Indo-Pacific region) were very small embryos. 

 Specimens of this species are characterized by strongly curled bodies 

 at this stage of development, and this, together with the paucity of 

 specimens, tends to negate apparent differences, such as orbital 

 diameter and length of second dorsal fin base, between specimens 

 from the Atlantic and Pacific regions (table 3). In addition, radio- 

 graphs of the chondrocrania show no apparent differences. For 

 these reasons, as well as the fact that neither of the other hammer- 

 heads of worldwide distribution {S. zygaena and S. lewini) show any 

 noticeable intraspecific differentiation, it seems best to recognize 

 but one species, Sphyrna mokarran. 



Range. — Sphyrna mokarran is circum tropical in distribution (map 

 1). However, it does not usually appear to be as common as Sphyrna 

 lewini, a species occupying a similar range. 



S. mokarran is found in the western Atlantic, including the Gulf 

 of Mexico and Caribbean Sea, from North Carolina south to Brazil. 



