. Bulletin of the United States Fish Commission. Fisheries -- United States; Fish-culture -- United States. 36 BULLETIN OF THE BUREAU OF FISHERIES 11. Mackerel shark (Isurus punctatus Storer) Blue shark; Porbeagle Jordan and Evermann {Lamna cornubica Grnelin), 1896-1900, p. 49. Garman, 1913, p. 36. Description.—The mackerel sharks (this and the two species following) are easily told from all the sharks so far mentioned by the shape of the tail, for while its lower lobe is sharklike, somewhat smaller than the upper, the difference is slight, the tail being almost evenly forked, with the upper l
. Bulletin of the United States Fish Commission. Fisheries -- United States; Fish-culture -- United States. 36 BULLETIN OF THE BUREAU OF FISHERIES 11. Mackerel shark (Isurus punctatus Storer) Blue shark; Porbeagle Jordan and Evermann {Lamna cornubica Grnelin), 1896-1900, p. 49. Garman, 1913, p. 36. Description.—The mackerel sharks (this and the two species following) are easily told from all the sharks so far mentioned by the shape of the tail, for while its lower lobe is sharklike, somewhat smaller than the upper, the difference is slight, the tail being almost evenly forked, with the upper lobe directed so sharply upward, the lower downward, that the tail as a whole is crescentic and much broader than long. In fact it recalls the tails of such pelagic bony fishes as the mackerel tribe or the swordfish in outline, likewise in its firm texture. More precise if less obvious a character is that the root of the tail bears a well marked longitudinal ridge or keel on either side, a feature shared by the white and basking sharks (pp. 39 and 41). This is a stout, heavy-shouldered shark, tapering in front to a sharply pointed snout and behind to a very slim tail root. Its dorsal and pectoral fins are very large; the former, originating over the armpit of the pectoral, is triangular and about as high as long; the latter, broad-based but tapering sicklelike to a narrow tip,. Fig. 12.—Mackerel shark (hurus punctatus). After Garman is only about half as broad as long. The second dorsal and anal fins are very small indeed, and the ventrals but little larger. The second dorsal stands over the anal. The positions of the dorsal fins are the readiest field mark to distinguish this species from the sharp-nosed mackerel shark (p. 38). The teeth are alike in the two jaws— small, slender, pointed, smooth-edged, and without spurs on the sides—and their structure differentiates this shark from the European porbeagle (Isurus nasus), which it otherwise resembles closely but in which
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Keywords: ., book, bookcentury1900, bookcollectionbiodiversity, bookdecade1920
