Ocypoda ceratophthalma belongs to the biological group of animals which, burrow for safety, but which must expose themselves above ground for feeding purposes. At these times the crabs are subject to attacks of predatory enemies. Such conditions place a premium upon speed, invisibility, and alertness. The high attainment of the first is as remarkable in these forms as is their fossorial activity on the one hand, and their extreme mental alertness and intelligence on the other. Correlated with this mode of life is the cryptic colouring, which is of protective value by day, and the nocturnal habit, which affords a measure of protection and invisibility by night. It is noteworthy that in many respects the Racing-Crab occupies among the Brachyura a biological position analogous to that held by the rabbit among the Rodentia.