THE FISHES OF PORTO RICO. 
63 
Family IV. SPHYRNID/F. The Hammer-head Sharks. 
General characteristics of the Galeidx, but with the head singularly formed, kidney-shaped, or 
Hammer-shaped, from extension of its sides, the nostrils being anterior and the eyes on the sides of 
the hammer; mouth crescent-shaped, under hammer; teeth of both jaws similar, oblique, each with 
a notch on the outside near base; no spiracles; last gill-opening over pectoral; first dorsal and pectorals 
large, the dorsal nearer pectorals than ventrals; second dorsal and anal small; a pit at root of caudal; 
caudal fin with a single notch toward its tip, its lower lobe developed. 
One genus, with 5 species, inhabiting most warm seas. Large sharks, known at once by the 
singular form of the head, which is not quite the same in any two species. 
Genus 5. SPHYRNA Rafinesque. 
Characters of the genus included above. In form of head there is a jierfeet gradation among the 
species from a narrow hammer, with the lobes three times as long as broad and deeply grooved along 
the anterior edge) to kidney shape, in which the anterior grooves are obsolete. Only one species of 
this genus is known from Porto Rico. 
n. Nostrils near eyes. 
b. Nostril with frontal groove short or obsolete; lateral extension of head moderate, so that the head is rather kidney- 
shaped than hammer-shaped. 
Reniceps: 
c. Nostril with groove obsolete; anterior and lateral margins of head confluent into a semicircle tiburo 
Platysqualus: 
ce. Nostril with a short groove; anterior margin of head curved, not continuous with lateral edges tildes 
Sphyrna: 
bb. Nostril with a well-developed groove, which extends along front of the hammer-shaped head, the anterior and 
posterior outlines of which are nearly parallel zygsena , 6 
6. Sphyrna zygasna ( Linmeus). Hammer-head Shark; “Cornuda.” 
Head truly hammer-shaped; width 41 f head about twice its length; length of hinder margin of 
hammer nearly equal to its width near eye, prolonged into a groove which runs along nearly the whole 
front margin of head; first dorsal large, second quite small, smaller than anal; pectoral rather large. 
Color, gray. A large, voracious shark, reaching a length of 15 feet or more; found in all warm seas; 
occasional on our coasts from Cape Cod and from Point Concepcion southward. Not obtained by us, 
but included on the authority of Professor Poey. 
Squalu< zygsena Linnseus, Syst. Nat., ed. X, 234, 1758, Europe: America. 
Cestracion zygsena, I’oey, Fauna Puerto-Riquena, 348, 1881; Stahl, Fauna de Puerto Kico, 81 and 107, 1883. 
Sphyrna zygsena, Jordan & Evermann, 1. c., 45, 1896. 
Fig, 3. — Prislis pectinatus. 
Family V. PRISTIDdi. The Saw-fishes. 
Body elongate, depressed; pectoral fin moderate, front margin quite free, not extending to head; 
snout produced into a very long, thin, flat blade, armed with series of strong tooth-like processes placed 
in sockets along each edge; teeth in jaws minute, obtuse; gill-openings moderate, inferior; spiracles wide, 
behind eye; nostrils inferior, no tentacles; no nictitating membrane; dorsal fins large, without spine, 
the first nearly opposite ventrals. Caudal well developed, bent upward, a fold along each side of tail. 
A single genus, with five or more species, inhabiting warm seas on sandy shores, sometimes 
ascending rivers. 
Genus 6. PRISTIS Latham. 
Characters of genus included above. 
a. Rostral teeth in 18 to 20 pairs: first dorsal chiefly before ventrals; caudal with a small lower lobe perrotteti 
aa. Rostral teeth in 24 to 32 pairs; first dorsal opposite ventrals; caudal without lower lobe pectinatus, 7 
