18/3] MR. R. B.WATSON ON MADEIRAN MOLLTJSKS. 371 



sided. Prom 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 truucated 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. 



Tnfa &%t Rissoa gibbera, Watson. (Plate XXXIV. fig. 7.) 



'f * 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, fiexuous, 

 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 fiexuous lines of growth, and with spiral 

 scratches, botli being excessively microscopic, superficial, and faint ; 

 they are best seen on labial varix. The 1| 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 1^ 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. 



Jf'horls 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* 



