The Atoll of Funafuti, Ellice group : its zoology, botany, ethnology and general structure based on collections made by Charles Hedley of the Australian Museum, Sydney, N.S.W.
Rissoina Polytropa, sp. nov. (Fig. 12)
Rissoina Polytropa, sp. nov. (Fig. 12).
Shell ovate, fusiform, narrow, white. Suture impressed. Whorls seven, Including two embryonec. The last whorl descends from whin it ascends suddenly and rapidly, the varix mounting up the preceding whorl for three tiers of spiral lyear. The shell id thus page 421thrown out of symmetry with most Rissoina. Sculpture—as usual with the genus, the longitudinal sculpture predominates to begin with; the third, or first sculptured, whorl showing a few stout plications. On the following whorl fine spiral threads are visible in the interstices; on the whorl beneath these are magnified to substantial lyræ and on the next or penultimate they have doubled in number, and rival the longitudinal in stature, at their intersection beads appear. On the last whorl the longitudinal, as such, have faded away, their influence showing in fine beads perceptible on the sutural and less distinct on a few of the nearer lyræ the spiral lyræ have now increased to nearly thirty, the anterior smooth, the posterior with evanescent beading. These are sharply raised threads, half the width of their interstices, evenly arranged, extending from the suture to the anterior point of the shell where they are smaller and more crowded. Aperture almost perpendicular, oval, anteriorly with a short perpendicular spout which falls short of the anterior margin; columella broad, obliquely and sharply truncated. From this truncation a wide and thick callus extends across the body whorl to the posterior angle of the aperture. Here the lip is sharply bent. The outer bevelled lip projects broadly as a heavy varix crossed by fifteen of the spiral lyrse, the central couple of which are smaller and nearer together. Length 4½, breadth 2 mm.
Five specimens in shallow water in the lagoon.
The extinction of longitudinal and the supremacy of spiral sculpture is unfrequent in the genus. Such species have been separated by Nevill as the Section Morchiella. From all there included the novelty differs by smaller size, more numerous lyræ, and truncated columella.