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Show 1873.] MR. R. B. WATSON ON MADEIRAN MOLLUSKS. 371 sided. From R. macandrece, var. spreta, it differs in being broader its basal rib is much stronger; its longitudinal ridges are fewer, sharper, more nodulous, with broader interspaces ; its spiral threads are finer and closer-set; the suture is interrupted by the longitudinal ridges; the apex is more truncated and lop-sided; outer lip is much thicker and externally knobbed ; mouth is slightly more oblique ; pillar-lip is scored by 3-4 instead of 2-3 twisted ribs. Mr. Jeffreys is inclined to consider this a variety of R. macandrece. RISSOA GIBBERA, Watson. (Plate XXXIV. fig. 7.) Shell. In outline almost a rectangle, with sides in the proportion of 3 to 4, the right slope of spire being parallel to base, and left slope to the edge of the mouth; solid, rising in steps with a huge umbilicus; dull. Sculpture. Ribs strong, narrow ('003 broad), high, sharp, flexuous, rising above the suture in a pointed shoulder or hunch and dying out on the base ; on lowest whorl about 12, including the enormous labial rib, one more and all straight on the previous whorl. The 1| whorl has none; and where they first begin to show they only appear on upper part of whorl below suture. The interspaces are from two to three times as broad as the ribs. Both interspaces and ribs are covered with longitudinal flexuous lines of growth, and with spiral scratches, both being excessively microscopic, superficial, and faint; they are best seen on labial varix. The l| whorl has 6 to 8 faint spiral lines in the substance of the shell. The 2nd whorl has a slight spiral thread round its base above the suture; this thread sometimes appears on base of shell below periphery. On base a heavy spiral ridge projects downwards ; it sweeps round the umbilicus, whose edge it forms, and at the point of the pillar is transformed uninterruptedly into the huge labial varix. Colour pure white to ruddy brown, often with a slight dusty bloom on the surface, and with four narrow bands slightly darker than the general tint, of which one close above and one close below periphery, one on base and one close to root of the basal ridge ; on upper whorls two, one in lower suture, and one in middle of whorl. The embryonic \\ whorl is always lighter in colour than the shell; so, too, is the basal ridge and the labial varix, though the latter is stained by the spiral bands of colour. Spire rising in strongly marked steps, ending in a blunt round top. The actual curve of the spire is deeply concave from the projection of the ribs on body-whorl; but the general impression produced by the two lines of the spire is that they meet at almost a right angle. Whorls 4 to 5, well rounded; but, from the hunch-like shoulder on the ribs below suture, each whorl seems to swell out suddenly above and then to contract below ; of regular increase until the last whorl, which is out of all proportion large. The extreme tip of the shell is turned in; and the apex is excavated, with a prominent margin. Suture almost quite straight, deeply excavated behind the hunches of the ribs, and a little channelled. 24* |