What is Balaena?

Legal Definition
Balaena is a genus of cetacean (whale) in the family Balaenidae. Balaena is considered a monotypic genus, as it has only a single extant species, the bowhead whale (B . mysticetus). It was first described in 1758 by Linnaeus, who at the time considered all of the right whales (and the bowhead) as a single species. Historically, both the family Balaenidae and genus Balaena were known by the common name, "right whales", however Balaena are now known as bowhead whales.

Throughout history, the family Balaenidae has been the subject of great taxonomic debate. Authorities have repeatedly recategorized the three populations of right whale plus the bowhead whale, as one, two, three or four species, either in a single genus or in two separate genera. In the early whaling days, they were all thought to be a single species, Balaena mysticetus. Eventually, it was recognized that bowheads and right whales were in fact different. Later, morphological factors such as differences in the skull shape of northern and southern right whales indicated at least two species of right whale—one in the Northern Hemisphere, the other in the Southern Ocean. As recently as 1998, Dale Rice, in his comprehensive and otherwise authoritative classification, Marine mammals of the world: systematics and distribution, listed just two species: Balaena glacialis (the right whales) and Balaena mysticetus (the bowheads).

A DNA study by Rosenbaum in 2000, and another study by Churchill in 2007 finally provided clear evidence to conclude that the three living right whale species do comprise a phylogenetic lineage, distinct from the bowhead, and that the bowhead and the right whales are rightly classified into two separate genera. The right whales, therefore, are now officially in the Eubalaena genus.

The fossil record of Balaena, dating to the late Miocene, encompasses ten species known from finds in Europe, North America, and South America. Balena, described by Scopoli in 1777, and Leiobalaena, described by Eschricht in 1849, are junior synonyms of Balaena.
-- Wikipedia
Legal Definition
A large fish, called by Black-stone a "whale." Of this the king had the head and the queen the full as a perquisite whenever one was taken on the coast of England. 1 Bl. Comm. 222.
-- Black's Law Dictionary
Legal Definition
A whale. See 1 Bl. Comm. 222.
-- Ballentine's Law Dictionary