MOLIUSCA OF THE ' CHALLENGER ' EXPEDITION. 595 



• marked with lines of gi'owtli and a few faint spirals ; while all 

 the rest of the shell without and within is brightly opalescent, 

 it is scarcely so at all. Height 0"3. B. 0-48, least 0'35. 

 Penultimate whorl 0-08. Mouth, height 0-2, breadth 0-23. 

 This specimen 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 (subg. 



Solariella, S. Wood) aureonitens, A. Ad., but is utterly different, 



not only in its angulation, but in its sculpture. 



2. Basilissa simplex, W. (simplex.) 



St. 323. February 28, 1876. Lat. 35° 39' S., long. 50° 47' W. 



Oif mouth of La Plata. 1900 fms. Grrey mud.. 1 specimen. 



Shell. — A rather narrow cone, with a flat base, 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 baud, about O'Ol 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 contiguous rounded threads occupying 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 of the umbilicus, being 

 specially so. Colour, the surface is a dead slightly creamy 

 white, formed by a thin calcareous layer through which the 

 underlying nacre shines. /S^iVe high and conical. Apexhroken. 

 Whorls 8 (reckoning the first two as broken), of slow and 

 regular increase till the last, which enlarges rapidly ; perfectly 

 flat, with an upper and lower border, sharj)ly angulated and 

 carinated at the periphery, slightly convex, but still very flat 

 on the base, with a bluntly angulated and carinated umbilical 

 edge. Suture linear, almost invisible, marginated above and 

 below. Mouth perpendicular, rhomboidal, with the body-pillar 

 and basal edges nearly equal, and the pillar and outer lip nearly 

 parallel. Outer lip sharp and thin, not patulous, not descend- 

 ing, advancing at its junction with the body-whorl, then re- 

 treating so as to form the broad open sinus, acute-angled at the 



