Elongate ocular peduncles have been independently evolved by many non-predatory, burrowing crabs. It is suggested that the burrowing habits of these crabs have provided the selective pressures for the evolution of these structures, primarily in the avoidance of predation whilst feeding on the surface. The development of elongate peduncles has necessitated structural modifications of the anterior carapace; in portunids these modifications are mainly of the anterolateral carapace margins, whilst in ocypodids and goneplacids they are mainly of the front. In the nineteenth century many authors, following Leach (1815), used as a convenient character by which to subdivide the Crustacea the presence or absence of ocular peduncles, thereby forming the Cstalk-eyed,' or podophthalmus, and the 'sessile-eyed,' or edriophthalmus, species; Bell (1853) and Bate & Westwood (1863, 1868) in their monographs on the British Crustacea are good examples. The presence of ocular peduncles is characteristic of, amongst others, the order Decapoda. In this group the peduncles generally extend for a distance equal to no more than one and a half times the length of the cornea; a number of brachyuran species, however, exhibit these structures in a greatly exaggerated form, the peduncles extending for a distance equal to about ten times the length of the cornea in some cases. Barnes (1967) briefly commented on the evolution of elongate ocular peduncles in one brachyuran genus, Macrophthalmus, and these comments may, in modified and extended form, be applicable to other brachyuran genera. The present paper will thus be concerned with the evolution of such structures in the Brachyura as a whole. This will be discussed in three sections: the distribution of elongate peduncles within the Brachyura; the selective pressures leading to their development; and the structural modifications of the carapace that have resulted from their evolution. THE GENERA