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



Shell. — Depressedly globose, with, a convexly conical spire, thin, translucent, horny, 

 nacreous in its whole texture, and iridescent on the surface, with a slightly reverted and 

 narrowly thickened lip, a thin-edged twisted pillar, the point of which runs out into a 

 bluntly mucronated angle. Sculpture : Longitudinals — the whole surface is covered 

 with strong, puckered, oblique lines of growth, which are sharp-edged but flattened, 

 rather regular, with many minuter ones in the intervals. The longitudinals are cross- 

 hatched with spirals, which are stronger and more regular, but not perfectly uniform, 

 consisting of square threads and furrows of equal breadth, and both scored by the 

 longitudinals ; on the earlier whorls these spirals disappear before the longitudinals do ; 

 and on the base they become on the outside feebler, closer, and finer, in the middle 

 broader and flatter, and stronger again toward the centre of the shell. Colour, delicate 

 yellowish, with a horny translucency and exquisite iridescence, which under the lens 

 appears brilliant. Spire high and slightly scalar. Apex very small, flatly rounded, the 

 embryonic 1^ whorl very slightly projecting. Whorls 7, of gradual increase, well rounded, 

 the last slightly angulated below, and on the base flattened, but rather less so towards 

 the mouth, where there is a slight contraction and downward turning of the whole whorl, 

 without, however, any descending of the lip at its junction with the body. Suture very 

 distinct, but not impressed. Mouth rather large, very oblique, semioval. Outer lip 

 reflected and thickened internally by a strong but narrow, equal, rounded, white pearly 

 callus, which almost disappears just at the upper corner, and which has a very slight furrow 

 round its margin ; it does not descend at all. Inner Up — from the corner of the outer 

 lip a very thin layer of nacre spreads out a little way across the body, but then ceases 

 entirely. The pillar is spread out at its base as a confined, flattened, unevenly inclined, 

 semicircular, iridescent umbilical pad, from the left corner of which the pfllar proper pro- 

 jects, with a narrow but rounded edge, twisted, straight, bending to the left, and advances 

 into a sharply angulated, and, as seen from behind, even mucronated junction with the 

 basal mouth-edge, to which the umbilical pad curving round the back of the pillar also 

 attains. The inside is scored with the external sculpture, and is brilliantly iridescent. 

 The umbilical pad is defined by a narrow furrow, and in front by a slightly tumid ridge, 

 which is the least nacreous part of the whole, shell. Operculum is membranaceous, 

 horny, yellowish, with about six to seven turns, each strongly defined by a narrow 

 line of thickening, and sharply scored with minute oblique radiating lines. H. 0"65 in. 

 B. 0-87, least 07. Penultimate whorl 0'199. Mouth, height 0-43, breadth 0-41. 



Unfortunately, though the operculum is preserved, nothing but traces of the animal remain within 

 the shell. 



