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.