and of about two whorls. Earliest whorls only lightly convex, but later ones become progressively more rounded; base convex. Aperture somewhat quadrate, not so oblique as in granosa Martyn. Outer lip sharp. Columella concave, oblique, iridescent. Height, 18 mm.; diameter, 15 mm.; height of spire, 10 mm. Locality—Pliocene beds of Kai Iwi (Castlecliffian), and Nukumaru (Nukumaruan). Holotype (Nukumaru) and two juvenile paratypes (Kai Iwi) in writer's collection. Readily distinguished from granosa Martyn by its smaller size, higher spire, less distended and less oblique aperture, and fewer and more regular spirals. Finlay (Trans. N.Z. Inst., vol. 57, pp. 366-7; 1927) drew attention to the fact that no Tertiary ancestors of Modelia and Lunella were up to that time known, stating that this was certainly due to the almost total lack of quite littoral fossil deposits in New Zealand, for the ancestors of such distinct shells must certainly have lived in the same locality. In 1928, however, Professor J. A. Bartrum and the writer collected several specimens of the new species from the mid-Pliocene beds at Nukumaru and at Kai Iwi, while still more recently Powell and Bartrum (Trans. N.Z. Inst., vol. 60, p. 413; Pl. 42, Fig. 63; 1930) describe and figure a shell allied to granosa Martyn, which they collected from beds of the Waitemata Series at Oneroa, Waiheke Island, the shallow-water facies of which is shown, as these writers point out (loc. cit., p. 396), by the presence therein of such genera as Haliotis, Cellana, Bembicium, Lepsiella, Pyrazus, Bankia. Genus Sinum Roeding, 1798. Type Helix haliotoidea Linné. Sinum marwicki n. sp. (Figs. 1, 4). Shell small, greatly depressed; whorls nearly three including a smooth, planorboid protoconch of one and a-half whorls; last whorl enlarging fairly rapidly; apex excentric and nearer front edge; spire flat, about one-fifth height of shell, and dorsal surface convex; body whorl lightly excavated ventrally between inner edge of aperture and outer margin of base, the concavity becoming more marked towards the small, partly hidden umbilicus. The upper surface has slightly undulating, somewhat flattened spiral threads, about 35 in number (3 per mm.), separated by grooves slightly wider than the ridges. Towards the periphery the last ten or so lirae suddenly become finer and the width of the interstices less in relation to that of the ridges. These are crossed by well-defined convex growth-lines. No spirals are developed on the base, but the lines of growth are prominent as they sweep convergingly into the umbilical tract. Suture markedly tangential. Aperture large, circular, nearly two-thirds greatest diameter of shell, angled above. Outer lip thin and strongly convex; inner lip covering parietal wall (callus partially broken away in specimen), reflexed and partly hiding umbilicus. Height, 5 mm.; greatest diameter, 14 mm.; least, 11 mm.