FAMILY SQUALID^ — CARCHARIAS. 349 



gums. Of the five branchial apertures, the posterior is smallest, and placed just anterior to or 

 slightly over the base of the pectorals. Upper maxillary bone detached from the snout, and 

 moves independently of it. 



The first dorsal high and triangular ; a foot high, and nearly as long on its base. Second 

 dorsal similar in shape, but much smaller. The pectorals long and wide, emarginated behind, 

 with a small process behind. Ventrals wider than high, and nearest the first dorsal. The 

 male organs arising from between the ventrals. Anal small, and placed behind the second 

 dorsal. Caudal composed of three distinct lobes'; one small, triangular, at the under side of 

 the tip of the elongated tail ; a second long and low, extending along the upper side of the 

 tail ; and a third short and broad, at the lower base of the tail. Vent between the ventrals. 



Color. Slate-blue above ; beneath soiled white, marked with obsolete bluish spots. Pupils 

 a longitudinal slit, edged with golden. In cabinet specimens, the color above becomes soiled 

 brown. 



Length, 12 feet. 



This Shark, which appears to be common to both sides of the Atlantic, is known here under 

 the various popular names of Thresher, Fox Shark and Swingle-tail. Its principal organ of 

 defence appears to be its long fle.xible tail : it assails, and literally threshes its enemies. It 

 pursues scholes of mackerel, mossbonkers and shad, and devours them in great numbers. 

 I refer to this species the individual roughly figured and described by Mitchill, although he 

 states inaccurately that the teeth were in a single row. 



This species has been noticed on our coast, from New-York to Nova Scotia. 



THE SMALL BLUE SHARK. 



Carcharias cerdleus. 

 plate lxi. fig. 200. 



The Small Blue Shark. MiTCHILL, Trans. Lit. and Phil. Soc. Vol. 1, p. 487. 



Characteristics. Small. Pectorals broad. Slate-blue above. Teeth small serrated. Length 

 two to six feet. 



Description. Body cylindrical ; deepest in front of the first dorsal fin. Surface covered 

 with minute, distant and vertically oblong scales ; under the lens, these appear as if fluted 

 longitudinally, and are elevated posteriorly, so as to be sensibly rough when the hand is passed 

 towards the head. Eyes rather large, lateral, with a large nictitating membrane. Nose blunt ; 

 conical. Nostrils lunate, directed downwards and backward, with a valvular fold of skin 

 beneath, and placed just under the margin of the snout, half way between its tip and the orbits. 

 Teeth in several series, small, triangular, serrate ; the interior edges convex. Branchial 

 apertures large, with the central one somewhat longest ; the penultimate over the anterior edge 

 of the pectoral, the last over the fin itself. 



