The heterogeneous assembly of Decapod Crustacean types classed as “Anomura” is well known to present a wide range of variation in structural features; in fact, the most apparent bond of union between its highly dissimilar sub-groups consists in the still greater disparity which exists between these and members of either “Macrura” or “Brachyura” proper. The Anomura may best be compared with that other heterogeneous group, the Amphibia: each, apparently of aquatic ancestry, has suffered in the unequal contest with a highly specialized offset from the parent-stock (Brachyura-Eeptilia); the survivors of both the ill-fated groups, Anomura and Amphibia, are few in number, varied in type, and probably not closely related among themselves.