, a new generic name and redescription of a stem balaenopteroid mysticete (Mammalia, Cetacea) from the Miocene of California.

Rorqual whales are among the most species rich group of baleen whales (or mysticetes) alive today, yet the monophyly of the traditional grouping (i.e., Balaenopteridae) remains unclear. Additionally, many fossil mysticetes putatively assigned to either Balaenopteridae or Balaenopteroidea may actually belong to stem lineages, although many of these fossil taxa suffer from inadequate descriptions of fragmentary skeletal material. Here we provide a redescription of the holotype of , a fossil balaenopteroid from the Monterey Formation of California, which consists of a partial cranium, a fragment of the rostrum, a single vertebra, and both tympanoperiotics. Kellogg (1922) assigned the type specimen to the genus Gray (1846), on the basis of its broad similarities to distinctive traits in the cranium of extant humpback whales ( (Borowski, 1781)). Subsequent phylogenetic analyses have found these two species as sister taxa in morphological datasets alone; the most recent systematic analyses using both molecular and morphological data sets place as a stem balaenopteroid unrelated to humpback whales. Here, we redescribe the type specimen of in the context of other fossil balaenopteroids discovered nearly a century since Kellogg's original description and provide a morphological basis for discriminating it from . We also provide a new generic name and recombine the taxon as , gen. nov., to reflect its phylogenetic position outside of crown Balaenopteroidea, unrelated to extant . Lastly, we refine the stratigraphic age of , based on associated microfossils to a Tortonian age (7.6-7.3 Ma), which carries implications for understanding the origin of key features associated with feeding and body size evolution in this group of whales.