Source : Webster's Revised Unabridged Dictionary (1913)

Sulphur-bottom \Sul`phur-bot"tom\, n. (Zo["o]l.)
   A very large whalebone whale of the genus {Sibbaldius},
   having a yellowish belly; especially, {S. sulfureus} of the
   North Pacific, and {S. borealis} of the North Atlantic; --
   called also {sulphur whale}.