362 NEW-YORK FAUNA. 



GENUS ZYG^NA. 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. 



Obs. 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. 



Ztqsna MALLSrS. 



PLATE LXn. FIR. 204, and a view of the under side. 



Hammer-headed Shark, Squalus zyg(Bna. Mitch:ll, Trans. Lit. and Phil. Soc. Vol. 1, p. 284. 

 Zygoma maXlaa. Valenciennes, Mem. du Mas. d' Hist. Nat. Vol. 9, p. 223, pi. 11, fig. 1 o 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 strise. 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- 



