n. pl.1.(Zool.) An order of Cephalopoda having four gills. Among living species it includes only the pearly nautilus. Numerous genera and species are found in the fossil state, such as Ammonites, Baculites, Orthoceras, etc.
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Group of the Molluscous Order Tetrabranchiata," Memoir of the Boston Society of Natural History 1.
Asexual reproduction and larval development in Polydora tetrabranchiata Hartman.