mens agree with Chilton's Enderby Island (Auckland Islands Group) in having the first antennae longer than the second. They are no doubt the same species On close examination, the Enderby specimens have proved to differ in so many points apart from those differences noted by Chilton that they must be considered a distinct species.

The shape of the sideplates is distinctive, those of the second gnathopod and the first and second peraeopods having a distinct triangular process; the first uropod rami are only half the peduncle length; the telson is distally convex, the third uropod is distinctive; the male first pleopod inner ramus is uniquely modified; and the epimeral plates are subrectangular, not trapezoid.

Undoubtedly, the most interesting feature of this genus is the unique series of modifications of the male first pleopod. To my knowledge, this is the only genus in the whole of the Order Amphipoda in which the pleopods are actually modified as distinct from reduced or degenerate. “The pleopods are perhaps less subject to variation throughout the two groups (Hyperiidea and Gammaridea) than any other part of the organism” (Stebbing, 1888). Wherever the pleopods are aberrant, other than in Chiltonia, it is by reduction or degeneration, not by a drastically new structural development as here.

That this happens only in the male, as far as can be seen, is analogous to the condition in the Isopoda where the male first pleopod is modified as a penis There is, too, some similarity in the shape and ornamentation of the ramus to that in the isopods, suggesting possibly that the modification serves the same purpose. Williamson (1951) points out that “in the Tahtridae the copulation positions make it impossible for the male to inject sperm directly into the female genital apertures. The male bears two short lateral penes on the ventral surface of the last thoracic segment.” Is it possible that this freshwater genus has modified pleopods to obviate this difficulty? But perhaps this is attributing too much to what may prove to be merely a peculiarity of shape.

Specimens of the Australian species which I was able to examine show no signs of this modification, but a more complete appraisal and description than they have hitherto been given is warranted Particularly useless for systematic purposes is Sayce's statement (1902) that C. subtenuis differs from C. mihiwaka by the more slender body and the larger head and eyes Barnard's description (1916) of the South African species does not mention the pleopods ^* Should the male pleopods be normal in these species, as seems likely, it may be necessary to raise them to subgeneric or even generic rank.