One species only is known (_C. rondeletii_), which is the most formidable of all Sharks. It is strictly pelagic; and appears to occur in all tropical and sub-tropical seas. It is known to attain to a length of 40 feet. The tooth figured here, of the natural size, is taken from a jaw 20 inches wide in its transverse diameter (inside measure), each half of the mandible measuring 22 inches.[36] The whole length of the fish was 36½ feet. Carcharodon teeth are of very common occurrence in various tertiary strata, and have been referred to several species, affording ample evidence that this type was much more numerously represented in that geological epoch than in the recent fauna. Some individuals attained to an immense size, as we may judge from teeth found in the Crag, which are 4 inches wide at the base, and 5 inches long, measured along their lateral margin. The naturalists of the “Challenger” expedition have made the highly interesting discovery that teeth of similar size are of common occurrence in the ooze of the Pacific, between Polynesia and the west coast of America. As we have no record of living individuals of that bulk having been observed, the gigantic species to which these teeth belonged must have become extinct within a comparatively recent period. Nothing is known of the anatomy, habits, and reproduction of the surviving species, and no opportunity should be lost of obtaining information on this Shark. [Illustration: Fig. 114.--Tooth of Carcharodon rondeletii.] ODONTASPIS.--The second dorsal and anal are not much smaller than the first dorsal. No pit at the root of the caudal. Side of the tail without keel. Mouth wide. Teeth large, awl-shaped, with one or two small cusps at the base. Gill-openings of moderate width. Large Sharks from tropical and temperate seas; two species. ALOPECIAS.--The second dorsal and anal very small. Caudal fin of extraordinary length, with a pit at its root. No keel on the side of the tail. Mouth and gill-openings of moderate width. Teeth equal in both jaws, of moderate size, flat, triangular, not serrated.