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Show 1884.] OF THE 'CHALLENGER ' EXPEDITION. 279 the total length. The peristome is thin, narrowly reflexed on left of the aperture, and rather broadly expanded in the umbilical region, and has the extremities, which converge but very slightly, connected by a thin callus spread over the whorl. Length 8 millimetres; diameter 3| ; length of aperture 2\, width 2. 5. BALEA (TRISTANIA) TRISTENSIS, Gray. Balea tristensis (Leach, MSS.), Gray, Zool. Journ. vol. i. p. 61, pi. vi. fig. A. Hab. Tristan d'Acunha, October 15, 1873. This species is more slender and longer than B. ventricosa, and has one and at times two additional whorls, which are more convex and more slowly enlarging. The characters of the sculpture, of the umbilicus, and aperture are very alike in both forms, the latter of course being shorter in proportion to the total length of the shell. SOUTH AMERICA. The few species collected on the mainland and adjacent islands are for the most part well known. It is curious to note that Limax gagates, which I have already recorded among the 'Challenger' collections from Bermuda, Tristan d'Acunha, and South Africa, is again found at the island of Juan Fernandez. On placing side bv side the specimens from these four localities, I am unable to trace any external difference. The species are the following :- 1. H. (STEPSANODA) QUADRATA, Ferussac. Hab. Juan Fernandez island. All the specimens brought home by the ' Challenger' differ slightly from those in Cuming's collection identified by Dr. Pfeiffer as belonging to this species. They are a little more depressed, just a trifle more widely umbilicated, and have a somewhat smaller aperture. 2. HELIX (STEPSANODA) SELKIRKI. (Plate XXIII. figs. 19-196.) Shell small, discoidal, deeply umbilicated, thin, pale, spotted above with red, irregularly streaked beneath with a lighter tint. Whorls 6-7, very narrow, tightly coiled, slowly increasing, convex, narrowly channelled at the suture, sculptured with close-set, hair-like lines of growth ; last whorl a little spreading towards the aperture, where it exhibits' a very faint depression or constriction near but a little above the middle ; spire flattened, only the least raised above the body-whorl. Aperture oblique, irregularly lunate; peristome simple, thin. Diam. 4 millim. ; height 2. Hab. Island of Juan Fernandez. This species is of the same size and general appearance as H. essellata, Muhlfeldt, from the same locality, and probably exists in ollections intermingled with that form. It is, however, distin- |