The Lamnoid or Mackerel Sharks.—The most active and most ferocious of the sharks, as well as the largest and some of the most sluggish, belong to a group of families known collectively as Lamnoid, because of a general resemblance to the mackerel-shark, or Lamna, as distinguished from the blue sharks and white sharks allied to Carcharias (Carcharhinus).
The Lamnoid sharks agree with the cat-sharks in the absence of nictitating membrane or third eyelid, but differ in the anterior insertion of the first dorsal fin, which is before the ventrals. Some of these sharks have the most highly specialized teeth to be found among fishes, most effective as knives or as scissors. Still others have the most highly specialized tails, either long and flail-like, or short, broad, and muscular, fitting the animal for swifter progression than is possible for any other sharks. The Lamnoid families are especially numerous as fossils, their teeth abounding in all suitable rock deposits from Mesozoic times till now. Among the Lamnoid sharks numerous families must be recognized.
The most primitive is perhaps that of the Odontaspididæ (called Carchariidæ by some recent authors), now chiefly extinct, with the tail unequal and not keeled, and the teeth slender and sharp, often with smaller cusps at their base. Odontaspis and its relatives of the same genus are numerous, from the Cretaceous onward, and three species are still extant, small sharks of a voracious habit, living on sandy shores. Odontaspis littoralis (also known as Carcharias littoralis) is the common sand-shark of our Atlantic coast. Odontaspis taurus is a similar form in the Mediterranean.
Family Mitsukurinidæ, the Goblin-sharks.—Closely allied to Odontaspis is the small family of Mitsukurinidæ, of which a single living species is known. The teeth are like those of Odontaspis, but the appearance is very different.
The goblin-shark, or Tenguzame, Mitsukurina owstoni, is a very large shark rarely taken in the Kuro Shiwo, or warm "Black Current" of Japan. It is characterized by the development of the snout into a long flat blade, extending far beyond the mouth, much as in Polyodon and in certain Chimæras. Several specimens are now known, all taken by Capt. Alan Owston of Yokohama in Sagami Bay, Japan. The original specimen, a young shark just born, was presented by him to Professor Kakichi Mitsukuri of the University of Tokyo. From this our figure was taken. The largest specimen now known is in the United States National Museum and is fourteen feet in length. In the Upper Cretaceous is a very similar genus, Scapanorhynchus (lewisi, etc.), which Professor Woodward thinks may be even generically identical with Mitsukurina, though there is considerable difference in the form of the still longer rostral plate, and the species of Scapanorhynchus differ among themselves in this regard.
Fig. 327.—Goblin-shark (Tenguzame), Mitsukurina owstoni Jordan. From a young specimen in the Imperial University of Tokyo.
Mitsukurina, with Heterodontus, Heptranchias, and Chlamydoselache, is a very remarkable survival of a very ancient form. It is an interesting fact that the center of abundance of all these relics of ancient life is in the Black Current, or Gulf Stream, of Japan.
