Head pointed—snout produced in form of a beak—a single crescent-shaped blowhole on top of head—one or two pairs of functional teeth in lower jaw—no teeth in upper jaw—greatest length, 30 feet. III. Family Delphinidæ. Porpoises. a. Subfamily Delphininæ. Medium size—two or more neck vertebræ joined—single crescent-shaped blowhole on top of head—teeth in both jaws—usually a high dorsal fin—greatest length, 30 feet. b. Subfamily Delphinapterinæ. White Whale and Narwhal. Medium size-head small and neck vertebræ all separated—single crescent-shaped blowhole on top of head—no dorsal fin-flippers very broad—greatest length, 20 feet. IV. Family Platinistidæ. Fresh Water Porpoises. Small size—neck vertebræ all separate—single crescent-shaped blowhole on top of head—all inhabit fresh or brackish water—greatest length, 12 feet. II. DIAGNOSES OF THE WHALES DESCRIBED IN THIS BOOK BLUE WHALE, SULPHURBOTTOM _Balænoptera musculus_ (Linn.) Very large size. Average length, 76 feet; maximum length, 87 feet. The pectoral fins are about 15 per cent. of the total length, falcate and bluntly pointed. The dorsal fin is small and variable in form, but usually more or less falcate; it is situated behind the line of the anus. Many ventral folds. The color of the body is mottled gray, the proportions of light and dark tints varying greatly in different individuals, but the body is usually lightest at the shoulder and between the flippers and the umbilicus. The head is a little darker than the body and unmarked. A few entirely white spots are usually present on the posterior ends of the abdominal folds. The pectoral fins are gray on the upper surface, except at the tip, and white below. The flukes are plain gray above, and below are marked with fine light and dark gray lines running antero-posteriorly. The dorsal fin is dark gray and the whalebone black. The rostrum of the skull is very broad with the free margins of the maxillæ convex; the nasal bones are oblong with truncated anterior margins. Vertebral formula: cervicals 7, dorsals 15 (–16), lumbars 14 (–16), caudals 26 (–28). Total, 63–65. Habitat: cosmopolitan. FINBACK, RAZORBACK _Balænoptera physalus_ (Linn.) Large size and very slender form. Average total length, 62 feet; the maximum, 81 feet. The pectoral fins are about 12 per cent. of the total length, lanceolate and pointed. The dorsal fin is moderate in height and falcate; it is situated just behind the line of the anus. Many ventral folds.