374 MR. R. B. WATSON ON MADEIRAN MOLLUSKS. [Mar. 18, 



strong relatively to thickness of shell, is cut off by a nick from 

 previous whorl, is very sinuous relatively to plane of spire, is very 

 faintly crossed by spiral threads. 



Spiral threads on body-whorl 7-9, transparent, prominent. The 

 first, nearest suture, always projects less than the others, and often 

 disappears, as does also the second occasionally. The fifth is the 

 prolongation of the suture. The seventh and eighth (sometimes it 

 is the sixth and seventh, rarely the eighth and ninth) are parted by 

 an interval deeper and wider than any of the others ; hence a hunch 

 on the base. The ninth merely encircles the pillar, and lies close to 

 the outer left margin of the mouth. On the third and on lower part 

 of the second whorls there are four of these threads ; in the second 

 whorl they are abruptly cut off; and above this, on the embryonic 

 shell, they are replaced by six microscopic hair-like spirals. The 

 interstices of the spiral threads are 3 to 4 times the breadth of the 

 threads, and are delicately but very closely tooled with excessively 

 minute undulated spiral scratches, of which about 4 go to ywoo m> 

 These cause the frosted appearance of the shell. When the longi- 

 tudinal ribs are present, the threads in crossing them form faint 

 knobs, and the whorl is cut into long narrow meshes. 



Colour pure white, transparent on the threads, frosted in the 

 intervals. 



Spire rises in steps, is short, blunt, and truncated, the tip being 

 turned in. 



Whorls 4-5, well-rounded, with a sloping shoulder below the 

 suture, of very regular increase. 



Suture deep and very straight. 



Mouth very open, large for size of shell, very triangular in conse- 

 quence of the extreme straightness of the line across the body and 

 from the flattening on the base. 



Lip thick, with a sharp projecting flange on the inward side. At 

 the outer lower corner it advances so much in front of the plane of 

 the mouth as almost to form a sinus and a channel. 



Inner lip projected (rather than reflected) on the pillar, so as to 

 form a distinct umbilical groove or chink. Across the body it 

 almost dies away, but reacbes the outer lip, which throws out a 

 slight pad to meet it. 



Sh. M. 5. 4. 3. 2. 1. 



L -06y -027 -034 -016 -009 "006 '002 



B -043 -025 -033 -037 '025 '015 '007 



Hab. Gorgulho, shore; Monte de Piedade (Cani^al), 15-35 

 fathoms ; Ponta de Sao Lourenco, 25-45 fathoms ; Funchal Bay, 

 50 fathoms ; Porto Santo, 50 fathoms. 



This species somewhat resembles R. subcarinata and R. auran- 

 tiaca. It differs from both in its broader form, whorls rising in 

 steps, large spoon-like and triangular mouth, deeper suture, fewer 

 and more rounded whorls, fewer spiral threads, the scrobicular 

 parting of two of these on the base, the abrupt apex with in-turned 

 tip, and its pure white colour. 



