Mary J. Rathbun (1860–1943) was an American zoologist, specialising in crustaceans. She was born on June 11, 1860 in Buffalo, New York the youngest of five children. Her mother died when she was only one year old, and Mary was therefore "thrown on her own resources". She was schooled in Buffalo, graduating in 1878, but never attended college. Mary first saw the ocean in 1881 when she accompanied her brother, Richard Rathbun, to Woods Hole, Massachusetts. He was employed as a scientific assistant to Addison Emery Verrill, alongside Verrill's chief assistant, the carcinologist Sidney Irving Smith. Mary helped label, sort and record Smith's specimens, and worked on crustaceans ever since.
For three years, Mary worked on a voluntary basis for her brother, before being granted a clerkship by Spencer Fullerton Baird at the Smithsonian Institution. She continued to work at the museum, largely unaided, and after 28 years, she was promoted to assistant curator in charge of the Division of Crustacea. Her largest work was Les crabes d'eau douce ("Freshwater crabs"), published in three volumes in 1904–1906. She wrote or co-wrote 166 papers in total, including descriptions of 1147 new species and subspecies, 63 new genera, one subfamily, 3 families and a superfamily, as well as other nomenclatural novelties. The taxa first described by Rathbun include important commercial species such as the Atlantic blue crab Callinectes sapidus, and the tanner crab, Chionoecetes bairdi. She retired on the last day of 1914, but did not stop working until her death. She qualified for a Ph.D. at George Washington University in 1917.