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 symphysis of the jaws to the middle of the belly is, as in other species, marked by furrows, forty to fifty-eight in number. The hairy covering is reduced (in an adult female) to thirteen hairs on each side of the lower jaw; in a foetus there were also seven hairs on each side of the upper jaw, as well as rather more on the lower jaw—altogether, forty-eight. This Whale appears to feed chiefly upon small Crustacea, especially the Copepod, Calanus finmarchicus. The number of baleen plates is about 330 on each side of the jaw. This Whale sometimes swims singly, but usually in schools of even as many as fifty.

Rudolphi's Rorqual (B. borealis) seems to be a perfectly inoffensive beast; it is said to be able to stay under water for as long a time as twelve hours.

A smaller species than the last is B. rostrata—at the outside 33 feet in length. Here the hairy covering is reduced to "two small hairs on the integument covering the apex of the lower maxilla." The colour is greyish black above, the underside white. On the other hand, B. sibbaldii, the Blue Whale, is the giant of its race, reaching a length of 85 feet. Its colour is a dark bluish grey, with small whitish spots on the breast. The dorsal fin is small and low with straight margins.

B. musculus, the Finner, is intermediate in size—not more than 70 feet. It seems doubtful whether the "sulphur bottom," B. australis, of Antarctica and B. patachonica differ specifically from this.

The genus Megaptera is very near Balaenoptera, but differs from it mainly in the following external and internal characters. The dorsal fin is not very prominent, and its place is taken by a lowish hump, whence, indeed, the common name of this Whale, "Humpback." The pectoral fin is unusually long, and the creature uses it to beat itself, the surrounding water, and, more playfully, its mates. The general outline of this Cetacean is more clumsy than that of Balaenoptera. The most important internal difference is in the form of the scapula, which has at most a slight acromion and coracoid process. These are rather more pronounced, according to Messrs. van Beneden and Gervais,