98 THE VOYAGE OF H.M.S. CHALLENGER. 



the last widens rapidly, is slightly rounded above, and still more slightly concave on the 

 base, with an acute, but still rounded keel. Suture impressed on the body-whorl, but on 

 the upper whorls sharply, though slightly, marginated below. Mouth a little oblique, 

 rhomboidal, the basal and palatal lines being nearly parallel, while the outer and inner 

 lips diverge downwards. Outer lip thin, not patulous, not descending, advancing at 

 its insertion, and then retreating so as to form a shallow, broad, open sinus a little 

 below the suture, acutely but roundedly angulate at the periphery, nearly flat on 

 the base, with a very slight nick at the point of the pillar, where it joins the inner 

 lip at a slightly obtuse angle. The pillar-lip is straight. It is a very little thickened, 

 and is slightly porcellanous. It advances a little on the edge of the umbilicus ; below 

 this it is hollow T ed out by a receding curve, but advances again into a slight rounded 

 projection just above its junction with the outer lip. In its whole direction it inclines 

 slightly to the left. Umbilicus oblique-edged, funnel-shaped, being wide in the mouth 

 and deep, with straight converging sides. It is slightly marked with lines of growth and 

 a few faint spirals ; while all the rest of the shell without and within is brightly opales- 

 cent, it is scarcely so at all. Height - 3 in. B. - 48, least 0"35. Penultimate whorl, 

 0-08. Mouth, height 0-2, breadth 0'23. 



The specimen from which this species is described is full grown, and the animal is still within 

 the shell, but the operculum is absent. 



The species has a slight general resemblance to Trochus (Solariclla) aurconitcns, A. Ad., but is 

 utterly different, not only in its angulation, but in its sculpture. In form it slightly recalls Zonites 

 cellarius, Mull. 



2. Basilissa simplex, Watson (PI. VII. fig. 6). 



Basilissa simplex, Watson, Prelim. Report, pt. 3, Journ. Linn. Soc. Lond., vol. xiv. p. 595. 



Station 323. February 28, 1876. Lat. 35° 39' S., long. 50° 47' W. Off mouth of 

 La Plata. 1900 fathoms. Blue mud. 



Shell. — A rather narrow flat-based cone, sharply angulated, small, thin, delicate, 

 smooth, glassy, nacreous under a thin white calcareous surface. Sculpture: There are 

 longitudinals, which are faint, hair-like, and sinuated, showing the old lines of growth. 

 Of spirals, faint, rounded, and irregular, the whole surface has traces. At the bottom of 

 each whorl is a flat puckered band, about 0"01 inch broad, whose upper edge projects 

 sharply, especially on the upper whorls, and whose lower edge is a slight narrow flange, 

 which forms a sharp carina at the periphery. This band forms the upper border of the 

 suture, which is further marginated below by two not continuous rounded threads occupy- 

 ing the top edge of each whorl. The base is covered by about fourteen rounded ridges 

 and furrows, which are rather stronger toward the centre, the last one, forming the edge 



