The color of the body is dark gray above and white below, the two colors merging imperceptibly into each other on the flanks. The coloration of the head is not bilaterally symmetrical, there being more white on the right side than on the left. The right side of the lower jaw is white and also the anterior third of the whalebone; the left side of the lower jaw and left baleen are dark gray. The gray of the flanks extends obliquely down and back from the pectoral fins toward the flanks, but does not reach the inferior edge of the peduncle, which is white. The pectoral fins are gray above and white below. The flukes are dark gray above and white below, with a gray posterior margin. The whalebone is gray, striped longitudinally with yellowish white in varying proportions; the anterior baleen on the right side is all yellowish white. The rostrum of the skull is narrow and pointed with the free margins of the maxillæ nearly straight. The nasal bones are narrow and pointed on the median line anteriorly. Vertebral formula: cervicals 7, dorsals 15 (–16), lumbars 14 (–15), caudals 25 (–26). Total, 61–63. Habitat: cosmopolitan. SEI WHALE, RUDOLPHI’S RORQUAL _Balænoptera borealis_ (Lesson) Moderate size. Average total length, 42 to 43 feet; maximum length, 53 feet. The dorsal fin is large, and falcate; it is situated just anterior to the line of the anus. Many ventral folds. The color of the head and back is dark gray; on the sides and flanks the gray of the back becomes lighter and the flanks are beautifully marked with wavy gray lines. The throat and breast are white, but a wide dark gray band runs across the belly. The ventral line from the anus to the flukes is gray. The pectoral fins above and below are dark gray, but somewhat lighter on the anterior half of the under side. The flukes above are dark gray like the back, and below are light gray in the ventral portion, becoming darker on the edges. The whalebone is bluish-black with white bristles. The rostrum of the skull is narrow and triangular with straight sides as in the Finback. The nasal bones are oblong and truncated anteriorly. The first rib is usually bifurcated. Vertebral formula: cervicals 7, dorsals 14 (–13), lumbars 13 (–14), caudals 22 (–23). Total, 56–57. Habitat: cosmopolitan. HUMPBACK _Megaptera nodosa_ (Bonn.) Form massive and ungraceful. Head flat and blunt with dermal tubercles’ along the sides and middle. Ventral folds few and broad. Average total length, 45 feet; maximum length, 55 feet. The pectoral fins are more than one-fourth the entire length with several prominent bunches along the anterior edge. The dorsal fin is low, thick and somewhat falcate, and the flukes are broad with crenate posterior edges.