All stages of Neobisium carpenteri and N. maritimum are described and compared. Details are given of the chaetal counts, measurements, ratios and morphological characters which can be used to distinguish the species. These are compared with the corresponding stages of N. muscorum (Gabbutt & Vachon, 1965). A study of the positions of the trichobothria, on the fingers of the chelae of the three species, during successive stages, indicates the approximate place at which the increments are added at the moults. The different positioning of these growth zones results in disparities in the disposition of the trichobothria in the adult condition. The importance of the relative positions of the trichobothria, as well as the stage at which certain trichobothria first appear, are discussed briefly in relation to the systematics of this order.