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Show 1873.] MR. R. B. WATSON ON MADEIRAN MOLLUSKS. 377 base ; from R. macandrewi in the number and narrowness of its longitudinal ribs, the greater depth of the suture, the greater swell of the whorls, the finer and more mucronated spiral threads, stain on apex and on lower lip corner ; from R. watsoni in greater size, especially of upper whorls, stronger and more regular ribs, stain on apex; from R. novarensis in being smaller, less tumid, less brilliant, ribs much fewer, spiral threads fewer and more strongly marked on the ribs, spire rising in steps. RISSOA NOVARENSIS, Watson. (Plate XXXV, fig. 13.) Shell conic-oval, not rising in steps, somewhat solid, glossy, brilliant, subopalescent. Sculpture. Longitudinal ribs, from 20 to 30, narrow, flexuous, about as wide as their intervals, diminishing in number on upper whorls and dying out on base. Labial rib thick and strong. Spiral threads on body-whorl about 14; they are slightly broader below than above periphery, where they are sometimes evanescent; they are about twice as broad as their interstices. Six of these usually appear on the penultimate whorl, but they become too indeterminate for counting. They are always most distinct in the rib-intervals; on the rib-crests they tend to evanesce. Besides these, the whole surface is covered with faint longitudinal lines ; and on the upper whorls especially exceedingly fine microscopic spiral lines can sometimes be traced. On the embryonic 1^ whorl about twelve closely and finely stippled spiral lines are visible. Colour yellowish white, opalescent on ribs, with three broad irregular and interrupted bands or series of spots of a clear yellowish brown, darkest near the mouth. The first is below the suture, the second at the periphery, the third on base. The first and second tend to coalesce behind the labial rib, at which point the third series also expands, crossing the rib and staining the lower outer corner of the mouth, the whole outer edge of which has a tinge of brown. The belly is yellow, and the whole pillar and labial rib an opaque white. The tip of the embryonic shell is a rich deep chestnut-brown. Spire a short broad cone, terminating in a blunt flattened apex in the centre of which the brown tip swells into sight. Whorls 4 to 5, very much flattened so as to form a continuous straight slope from tip to periphery, of rather rapid increase. Suture straight, shallow, narrow, but very distinct. Mouth oval, very little pointed above, contracted on its outer upperside, but expanded on base. Outer lip thickened by a heavy white rib, somewhat incurved above, and there bevelled off from the outside to a sharp edge, whereas on the base the bevelling-off is from the inside entirely. This labial rib lies a little way back from the edge; and beyond it the sharp mouth-edge is only scored by fine longitudinal lines. Inner lip is barely detached from the pillar, so as to leave a slight chink ; it is continued pretty thickly across the belly, and meets the outer lip in a rounded and somewhat padded angle. |