P T Barnum's agent
Francis Talbot Day was an army surgeon and naturalist in the Madras Presidency who later became the Inspector-General of Fisheries in India and Burma. A pioneer ichthyologist, he described more than three hundred fishes in the two-volume work on The Fishes of India. He also wrote the fish volumes of the Fauna of British India series. He was also responsible for the introduction of trout into the Nilgiri Hills, for which he received a medal from the French Societe d'Acclimatisation. Many of his fish specimens are distributed across museums with only a small fraction deposited in the British Museum (Natural History), an anomaly caused by a prolonged conflict with Albert Günther, the keeper of Zoology there
Naturalist
Charles Culliford Boz Dickens, better known as Charles Dickens Jr., was the first child of the English novelist Charles Dickens and his wife Catherine. A failed businessman, he became the editor of his father's magazine All the Year Round, and a writer of dictionaries. He is now most remembered for his two 1879 books, Dicken's Dictionary of London and Dickens's Dictionary of the Thames
Herbert Thomas Dicksee was an English painter who specialised in oil paintings of dogs, particularly the deerhound
Felix Anton Dohrn was a prominent German Darwinist and the founder and first director of the first zoological research station in the world, the Stazione Zoologica in Naples, Italy.