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Show 278 MR. E. A. SMITH ON THE MOLLUSCA [May 6, TRISTAN D'ACUNHA. Until now the known land-mollusks from these islands consisted of the two species of Balea mentioned below. The discovery therefore of three additional terrestrial forms is particularly interesting, two of them, however, being also found elsewhere. The species are :- 1. LIMAX CANARIENSIS, d'Orbigny. Several specimens from the above locality agree in all external characters with those from Teneriffe which I have identified with this species. As a rule they are reticulated and mottled on the back with black, but in one or two instances this colouring is almost entirely absent. 2. LIMAX GAGATES, Draparnaud. A single specimen, in contraction three quarters of an inch in length, appears to agree externally in every respect with this well-known European form. It has also been recorded from the Azores, Madeira, St. Helena. 3. HELIX (HYALINIA) EXULATA. (Plate XXIII. figs. 18, 18 6.) Shell depressed, orbicular, thin, moderately widely and deeply umbilicated, semitransparent, pale yellowish horn-colour, glossy, sculptured with oblique curved lines of growth. Whorls 5, convex above, distinctly margined below the suture, rather rapidly enlarging, the last not descending in front. Spire very depressed, only a little raised above the body-whorl, terminating at the apex in a large nuclear volution which is scarcely at all elevated above the succeeding one. Aperture broadly lunate, slightly oblique ; peristome thin, a very little thickened and expanded on the columellar side. Greatest diameter 7\ millim., smallest 6|, height 4. Hab. Tristan d'Acunha. Although several species from various parts of the world bear considerable resemblance to this little unpretending form, still none are apparently identical. 4. BALEA (TRISTANIA) VENTRICOSA, Gray. Balea ventricosa (Leach MSS.), Gray, Zool. Journ. vol. i. p. 62, pi. vi. fig. B. Hab. Inaccessible Island, Tristan d'Acunha, October 16, 1873. This species has not, as far as I can ascertain, ever been fully characterized, the diagnosis of Gray, consisting of five words only, being totally inadequate. It may be described as pupiform, pale olive-brown, narrowly rimate, sculptured with rather strong oblique lines of growth. The whorls are six and a half to seven in number, rather rapidly enlarging, convex, divided by a deep oblique suture. The spire has curved outlines, and terminates above in an obtuse rounded smooth apex. The aperture is rather large, and occupies somewhat less than a third of |