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.
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.