362 NEW-YORK FAUNA. 
GENUS ZYGAINA. Cuvier. 
Head flattened horizontally, truncated or convex in front, with the sides very much extended 
laterally, appearing hammer-shaped. The eyes placed on the extremities of the lateral 
prolongations ; the nostrils at their anterior margins ; mouth beneath. 
Oxzs. This genus now comprises about five species. The existence of a species on the 
coast of the United States has hitherto been only briefly indicated. 
THE HAMMER-HEAD SHARK. 
ZYGENA MALLEUS. 
PLATE LXII. FIG. 204, anp A VIEW OF THE UNDER SIDE. 
Hammer-headed Shark, Squalus zygena. Mitcuiuu, Trans. Lit. and Phil. Soc. Vol. 1, p. 284. 
Zygena malleus. VALENCIENNES, Mem. du Mus. d’ Hist. Nat. Vol. 9, p. 223, pl. 11, fig. 1 a and 1 6 
Characteristics. Head three times broader than long. Second dorsal over, slightly behind 
the anal. Posterior branchial aperture over the base of the pectorals. 
Length four to eleven feet. 
Description, from a young specimen caught in the harbor of New-York. Body cylindrical, 
elongated. Surface rough when rubbed forwards ; under the lens, it appeared to be covered 
with plates, fluted with minute deep parallel striae. Head elongated transversely, somewhat 
convex, above three times broader than long; the anterior margin describing irregularly the 
arc of a large circle ; the posterior margin is rendered straight, thin and submembraneous, by 
an expansion of the integuments; the lateral margin forming almost a right angle with the 
anterior edge. Eyes large, and furnished with a lid which is attached to the internal portion 
of the base of the orbit; the eyes are placed near the angle formed by the anterior and lateral 
margins, in such a manner as to enable the animal to look*above and beneath. Nostrils 
placed in a deep notch near the angle; they form an oblique slit, partially covered by an 
acutely pointed process, which is continued by a long and deep furrow along the anterior 
margin. Mouth crescent-shaped, with three rows of white hyaline teeth above and below. 
Teeth above triangular, acute, not serrated; their tips directed outwards from the centre, 
with a shoulder on the outer side; in the centre, a few with shoulders on both sides. All 
the branchial apertures short and small; the posterior smallest, and placed over the base of 
the pectorals. 
The first dorsal quadrilateral ; its origin slightly behind the base of the pectorals, higher 
than wide, deeply concave behind, and pointed at its posterior tip. Second dorsal rhom- 
boidal, very small, with its posterior tip acutely drawn out behind ; its base extends beyond 
a point vertical to the posterior extremity of the base of the anal. Pectorals placed low down, 
subtriangular, broad, distant and slightly concave behind. Ventrals small, broad, nearly mid- 
