48 Bulletin 47, United States National Museum. 



Subgenus ISUROPSIS, Gill. 

 65. ISURUS DEKAYI, (Gill). 



(MACKEREL SHARK.) 



Head 5 in length to tip of caudal ; pectoral as long as head, a little 

 longer than upper caudal lobe. Dorsals and pectorals falcate ; first dorsal 

 inserted behind pectoral at a distance equal to^ head ; base of first dorsal 

 2 in head, its height If. Middle teeth very long, much longer and 

 narrower than lateral teeth. Dark bluish gray above, white below, the 

 color abruptly changing on the tail ; upper fins dusky, lower pale. 

 L. 10 feet. Cape Cod to West Indies, not common ; described here from 

 a specimen taken at Pensacola. The American species seems to differ from 

 the Asiatic L glaucus in its longer pectorals and higher dorsal. (Named 

 for James E. De Kay, author of the Fauna of New York.) 



Lamna punctata, DE KAY, N. Y. Fauna: Fishes, 352, 1842, New York, (not Squalus punciatus, 



MITCHILL). 



Isuropsis dekayi, GILL, Ann. Lye. Nat. Hist. N. Y., 1861, 153, after De Kay. 

 huropsis glaucus, POEY, Synopsis, 446, 1868 (not Oxyrhina glauca, MULLER & HENLE). 

 Isurus dekayi, JORDAN & GILBERT, Synopsis, 874, 1883. 



Subgenus ISURUS. 



66. ISURUS OX YRHYNCHUS, Eafinesque. 

 (MACKEREL SHARK ; PESCE TONDO ; CANE DI MAEE.) 



Muzzle long and pointed, the preoral portion of the snout as long as 

 the cleft of the mouth and greater than interorbital space; snout in 

 the form of a cone flattened below; spiracles very small. Teeth -\l on 

 each side, long, lanceolate, without basal cusps; third tooth on each side 

 of upper jaw much smaller than that next to it. Gill openings very 

 wide, the width of the first rather more than its distance from the 

 last. Origin of dorsal close behind base of pectorals, which are falci- 

 form, the length of the lower margin that of the upper ; second dorsal 

 very small, opposite the anal and of the same size ; caudal lunate, the 

 upper lobe i longer than the lower. Size very large. A voracious shark, 

 similar in habits to Isurus deJcayi, from which it differs in the back- 

 ward position of the dorsal; from Lamna cornubica it is separated by the 

 absence of lateral denticles on the teeth. Mediterranean Sea and neigh- 

 boring parts of the Atlantic, probably occasionally straying to our coast, 

 as the description of the large shark published by Capt. Nathaniel E. 

 Atwood, under the name of Carcharias tigris, * could refer to no other 

 known species. (6$>f, sharp; /Suy^of, snout.) (Eu.) 



* Capt. Atwood describes this specimen, which was 8 feet 10 inches in length, as dark blue 

 above, an irregular lead-colored lateral band ; belly white. Largest teeth 1^ inches long, % 

 inch broad at base, smooth (edged) and curving upward. Snout pointed, 2 feet long, from 

 first gill opening : branchial apertures 9 inches long, the distance from first to last 5 inches; 

 7% inches between the eyes; nostrils 2% inches before eyes. Front of first dorsal 3 inches 

 behind pectorals; it is 13 inches high and 12 long at base, the free posterior edge 2% inches. 

 Second dorsal 25 inches behind posterior root of first, 2% inches high, 4 inches long ; pectorals 

 23 inches high, 11% broad at base; ventrals inserted at a point midway between the two dorsals; 

 anal similar to second dorsal, inserted an inch farther back. Upper lobe of caudal 23 inches 

 long, lower 18 ; the distance between the tips 31 inches. "The first specimen of this very rare 

 'shark was brought from the Gulf of Mexico and presented to the State Cabinet, the second was 

 taken at Truro and presented to the Museum of Comparative Zoology ; the third, which had 

 bitten off and swallowed largo portions of a sword fish, was captured in 1864, at Provincetown 

 and given to the (Hoston) Society ; a fourth specimen, and the one described above, at Province- 

 town in August last." Atwood. 



