Fishes of the Western North Atlantic 285 



but an occasional tooth smooth-edged and others partially so; an irregular group of 2 to 4 

 teeth at the lower symphysis, much smaller than those on either side and with relatively 

 narrower bases; i to 2 rows of teeth functional in front and i in the sides of mouth in upper 

 jaw; I to 3 rows functional in front and i row laterally in lower jaw. 



Anterior margin of first dorsal about as long as snout in front of mouth, its origin 

 posterior to inner corner of pectoral by a distance about % as long as its anterior margin 

 and about midway between tip of snout and precaudal pit, the midpoint of its base at a 

 vertical a little less than % (about 70%) as far from origin of pelvics as from axil of 

 pectoral ; its anterior margin nearly straight, apex rounded, its posterior margin deeply con- 

 cave toward the base, its free rear corner moderately acute, sharp-tipped, about % as long 

 as its base. Second dorsal about Yi as long at base as ist, and less than Vs as large in area, 

 its posterior margin less deeply concave, but its free rear corner more slenderly pointed 

 and about as long as the base, its origin about over or very little posterior to origin of anal. 

 Caudal about V4 of total length or a little more, its axis moderately raised, its terminal 

 sector slender with pointed tip, the subterminal notch strongly marked, its lower anterior 

 corner expanded as a blunt-tipped lobe, about V2 as long as the upper margin of fin. Anal a 

 little larger than 2nd dorsal, its anterior margin convex, apex rounded, its posterior margin 

 very deeply concave, its free rear corner acutely pointed and about % as long as its base. 

 Pelvics only about as large in area as anal, or a little larger, with nearly straight anterior and 

 inner margins, slightly concave distal margins and narrowly rounded corners. Pectoral 

 noticeably long, being about as long as head to 5th gill opening in medium-sized and large 

 specimens, but relatively somewhat shorter in small ones,'"^ only a little more than ^/3 

 as broad as long, tapering toward tip, its anterior margin moderately convex (more 

 strongly so in small specimens), the inner margin moderately concave proximally, the 

 apex very narrowly rounded, the inner corner more broadly so. 



Color. Living and freshly caught specimens are dark indigo blue along the back, 

 shading to a clear bright blue" along the sides, and to snow white below; the tips of the 

 pectorals are usually dusky and the anal partly so. But the beautiful blue of the back and 

 sides darkens to a slaty or sooty gray soon after death. 



Size. The Blue Shark is reputed to reach a length of 20 feet and commonly 1 5 feet. 

 Actually, however, about 12 feet 7 inches (3.83 m.) is the longest of which we have found 

 positive record; an i i-foot specimen is the longest we have handled. Embryos as large as 

 350 to 450 mm. have been recorded, and free living specimens as small as 2 1 to 36 inches 

 (539 mm.; 661 mm.; 910 mm.; see Study Material, p. 282). The sizes of the females in 

 which young have been found suggest that this Shark does not mature until a length of at 

 least seven to eight feet is reached. Corresponding to their slender build. Blue Sharks 

 are less heavy, length for length, than the more stout-bodied species; probably the follow- 

 ing weights at different lengths, collected from various sources, are representative : 6 to 7 



12a. 15.4 to 17.1 per cent of total length in three specimens, 539 to 910 mm. long. 

 13. "Sailor Blue" in Ridgway, Color Standards and Color Nomenclature, 1912: pi. 21. 



