50 
BULLETIN OF THE BUREAU OF FISHERIES 
on posterior edge; first dorsal behind the origin of the pectorals and in advance of the ventrals; 
second dorsal over the anal; caudal pits present; lower lobe of caudal produced, upper lobe long. 
KEY TO THE SPECIES' 
a. Head very broad, its greatest width about 3 in total length; anterior outline of head irregular, 
a deep concavity over each nostril zygsena, p. 50 
aa. Head less broadly expanded, its width about 5 in the total length; anterior outline of head 
regularly convex, no concavity over nostrils tiburo, p. 51 
8. Sphyrna zygaena (Linnaeus). Hammerhead shark. 
Sgualus zygxna Linnaeus, Syst. Nat., ed. X, 1758, p. 234; America. 
Sphyrna zygxna Lugger, 1877, p. 88; Jordan and Everinann, 1896-1900, p. 45. 
Cessation zygxna Garman, 1913, p. 157, pi. 1, figs. 1 to 3. 
Body elongate, compressed; head very broad, hammer-shaped, the front margin broadly 
and irregularly convex, with a deep concavity at each nostril; width of head at eyes from 3 to 
3.25 in total length; nostril close to eye, with a long groove on margin of snout; mouth moderate, 
its width a little shorter than preoral length of snout; teeth similar in both jaws, oblique, cusps 
triangular, the lateral ones with a notch at base posteriorly; first dorsal high, its height greater 
than the length of its base, the outer margin concave, its origin a little behind axil of pectoral; 
second dorsal small, its posterior angle notably produced; upper lobe of caudal long, the lower 
lobe also produced, its length about 2.75 in the upper lobe; anal fin a little longer than the second 
dorsal, the outer margin deeply concave, its origin a little in advance of the second dorsal; ventral 
Fig. 28.— Sphyrna zygxna 
fins small, inserted slightly more than half as far from origin of anal as from base of pectoral; pectoral 
fins moderate, scarcely reaching to base of first dorsal, the lower angle not produced and the pos- 
terior margin of fin slightly concave. 
Color of fresh specimen lead gray above, lower parts grayish white; tips of pectorals black; 
the tips of the other fins dark. 
No specimens of this shark were preserved. The description herewith was compiled from 
published accounts. 
Lugger (1877, p. 89) states that the hammerhead shark was so very common in the mouth of 
Miles River, Md., during the summer of 1876 that the fishermen were forced to abandon that 
ground. The species is not reported by other observers. During the present investigation only 
three individuals were seen. A hammerhead was taken on July 15 and another one on July 17, 
1916, in pound nets in Lynnhaven Roads, and in the same locality a 2-foot specimen was caught 
with hook and line on June 26, 1921. 
The food of this shark, according to stomach examinations made by investigators at Beaufort, 
N. C., consists of fish and crustaceans. Gudger (1907, pp. 1005-1006) took an almost perfect 
skeleton and many fragments of skeletons of the sting ray ( Dasybatus say ) from the stomach of a 
specimen of this shark, and he found imbedded in various parts of the shark numerous spines of 
the sting ray. In all, 50 spines were extracted, mainly from the mouth parts, and, according to 
this author, all that were present quite certainly were not recovered. This particular shark was 
harpooned while it was in pursuit of a sting ray and the evidence would suggest that this sting ray 
may form a considerable part of the food of this species of shark. 
Lf, 
uPLy 
